I managed to reproduce the issue again. It's still not consistent, but here's what I did:

1. Have Boinc Manager running for a long time, doing tasks, etc.
2. Activity -> Suspend
3. File -> Exit Boinc Manager
4. Go play PC games for ~1 hour.
5. Stop playing PC games.
6. Start up Boinc Manager.
7. Boinc Manager get stuck on "Connecting to localhost".

I also noticed that while in this state, the Tools -> Event Log option is greyed out.

Depending on the number of projects and total number of file in the projects data folders, it can show for several minutes the "waiting message", before it disappears and you have control of BOINC.

You need to get the first 30 or so lines from the stdoutdae.txt FILE located in the BOINCDATA folder a few minutes after BOINC is restarted, not from the ,BOINC Manager console. The file is by default located in C:\ProgramDats\BOINC\ which might be a hidden folder.

Use a text editor to open the file such as notepad.exe

Highlight the first 30 lines, copy and paste into a new message in this topic and post your reply.

Here is the entire file:

23-Mar-2023 15:20:53 [---] cc_config.xml not found - using defaults
23-Mar-2023 15:20:53 [---] Starting BOINC client version 7.20.2 for windows_x86_64
23-Mar-2023 15:20:53 [---] log flags: file_xfer, sched_ops, task
23-Mar-2023 15:20:53 [---] Libraries: libcurl/7.84.0-DEV Schannel zlib/1.2.12
23-Mar-2023 15:20:53 [---] Data directory: C:\ProgramData\BOINC
23-Mar-2023 15:20:53 [---] Running under account User
23-Mar-2023 15:20:53 [---] OpenCL: AMD/ATI GPU 0: AMD Radeon RX 6900 XT (driver version 3380.6 (PAL,LC), device version OpenCL 2.0 AMD-APP (3380.6), 16368MB, 16368MB available, 20634 GFLOPS peak)
23-Mar-2023 15:20:53 [---] OpenCL: Intel GPU 0: Intel(R) UHD Graphics 770 (driver version 31.0.101.4091, device version OpenCL 3.0 NEO, 12972MB, 12972MB available, 410 GFLOPS peak)
23-Mar-2023 16:41:18 [---] cc_config.xml not found - using defaults
23-Mar-2023 16:41:18 [---] Starting BOINC client version 7.20.2 for windows_x86_64
23-Mar-2023 16:41:18 [---] log flags: file_xfer, sched_ops, task
23-Mar-2023 16:41:18 [---] Libraries: libcurl/7.84.0-DEV Schannel zlib/1.2.12
23-Mar-2023 16:41:18 [---] Data directory: C:\ProgramData\BOINC
23-Mar-2023 16:41:18 [---] Running under account User
23-Mar-2023 16:41:18 [---] OpenCL: AMD/ATI GPU 0: AMD Radeon RX 6900 XT (driver version 3380.6 (PAL,LC), device version OpenCL 2.0 AMD-APP (3380.6), 16368MB, 16368MB available, 20634 GFLOPS peak)
23-Mar-2023 16:41:18 [---] OpenCL: Intel GPU 0: Intel(R) UHD Graphics 770 (driver version 31.0.101.4091, device version OpenCL 3.0 NEO, 12972MB, 12972MB available, 410 GFLOPS peak)

As you can see there's a pile of information about what has started, how things are configured. The easiest way to get this is very soon after a re-boot of the computer, say five minutes, or (as in my case) have a very large event log.

The problem is that if I reboot my PC, then the issue goes away (as I've previously stated).

Not sure if directly caused by, but strongly correlated for now:

I noticed my Docker Desktop for Windows was outdated. So I went to update it, and then it got stuck on "Docker desktop stopping". I also tried running some wsl commands, but they all hung.

I came across this Github thread: https://github.com/microsoft/WSL/issues/4144
as well as this Stackoverflow post: https://stackoverflow.com/questions/70567543/cant-restart-wsl2-lxssmanager-hangs-in-stopping-state-how-to-restart

I ran command `tasklist /svc /fi "imagename eq svchost.exe" | findstr LxssManager`, noted the PID, then went to Task Manager and killed the Service Host task with that PID.
Then Docker Desktop stopped correctly, and updated. Then I started up Boinc Manager and suddenly it worked just fine, projects/tasks loaded, etc.

Here's the stdoutdae.txt again:

-------------------------------------------------------
23-Mar-2023 15:20:53 [---] cc_config.xml not found - using defaults
23-Mar-2023 15:20:53 [---] Starting BOINC client version 7.20.2 for windows_x86_64
23-Mar-2023 15:20:53 [---] log flags: file_xfer, sched_ops, task
23-Mar-2023 15:20:53 [---] Libraries: libcurl/7.84.0-DEV Schannel zlib/1.2.12
23-Mar-2023 15:20:53 [---] Data directory: C:\ProgramData\BOINC
23-Mar-2023 15:20:53 [---] Running under account User
23-Mar-2023 15:20:53 [---] OpenCL: AMD/ATI GPU 0: AMD Radeon RX 6900 XT (driver version 3380.6 (PAL,LC), device version OpenCL 2.0 AMD-APP (3380.6), 16368MB, 16368MB available, 20634 GFLOPS peak)
23-Mar-2023 15:20:53 [---] OpenCL: Intel GPU 0: Intel(R) UHD Graphics 770 (driver version 31.0.101.4091, device version OpenCL 3.0 NEO, 12972MB, 12972MB available, 410 GFLOPS peak)
23-Mar-2023 16:41:18 [---] cc_config.xml not found - using defaults
23-Mar-2023 16:41:18 [---] Starting BOINC client version 7.20.2 for windows_x86_64
23-Mar-2023 16:41:18 [---] log flags: file_xfer, sched_ops, task
23-Mar-2023 16:41:18 [---] Libraries: libcurl/7.84.0-DEV Schannel zlib/1.2.12
23-Mar-2023 16:41:18 [---] Data directory: C:\ProgramData\BOINC
23-Mar-2023 16:41:18 [---] Running under account User
23-Mar-2023 16:41:18 [---] OpenCL: AMD/ATI GPU 0: AMD Radeon RX 6900 XT (driver version 3380.6 (PAL,LC), device version OpenCL 2.0 AMD-APP (3380.6), 16368MB, 16368MB available, 20634 GFLOPS peak)
23-Mar-2023 16:41:18 [---] OpenCL: Intel GPU 0: Intel(R) UHD Graphics 770 (driver version 31.0.101.4091, device version OpenCL 3.0 NEO, 12972MB, 12972MB available, 410 GFLOPS peak)
23-Mar-2023 16:53:24 [---] cc_config.xml not found - using defaults
23-Mar-2023 16:53:24 [---] Starting BOINC client version 7.20.2 for windows_x86_64
23-Mar-2023 16:53:24 [---] log flags: file_xfer, sched_ops, task
23-Mar-2023 16:53:24 [---] Libraries: libcurl/7.84.0-DEV Schannel zlib/1.2.12
23-Mar-2023 16:53:24 [---] Data directory: C:\ProgramData\BOINC
23-Mar-2023 16:53:24 [---] Running under account User
23-Mar-2023 16:53:24 [---] OpenCL: AMD/ATI GPU 0: AMD Radeon RX 6900 XT (driver version 3380.6 (PAL,LC), device version OpenCL 2.0 AMD-APP (3380.6), 16368MB, 16368MB available, 20634 GFLOPS peak)
23-Mar-2023 16:53:24 [---] OpenCL: Intel GPU 0: Intel(R) UHD Graphics 770 (driver version 31.0.101.4091, device version OpenCL 3.0 NEO, 12972MB, 12972MB available, 410 GFLOPS peak)
23-Mar-2023 17:08:24 [---] cc_config.xml not found - using defaults
23-Mar-2023 17:08:24 [---] Starting BOINC client version 7.20.2 for windows_x86_64
23-Mar-2023 17:08:24 [---] log flags: file_xfer, sched_ops, task
23-Mar-2023 17:08:24 [---] Libraries: libcurl/7.84.0-DEV Schannel zlib/1.2.12
23-Mar-2023 17:08:24 [---] Data directory: C:\ProgramData\BOINC
23-Mar-2023 17:08:24 [---] Running under account User
23-Mar-2023 17:08:24 [---] OpenCL: AMD/ATI GPU 0: AMD Radeon RX 6900 XT (driver version 3380.6 (PAL,LC), device version OpenCL 2.0 AMD-APP (3380.6), 16368MB, 16368MB available, 20634 GFLOPS peak)
23-Mar-2023 17:08:24 [---] OpenCL: Intel GPU 0: Intel(R) UHD Graphics 770 (driver version 31.0.101.4091, device version OpenCL 3.0 NEO, 12972MB, 12972MB available, 410 GFLOPS peak)
23-Mar-2023 17:08:27 [---] Windows processor group 0: 24 processors
23-Mar-2023 17:08:27 [---] Host name: DESKTOP-MFSEP24
23-Mar-2023 17:08:27 [---] Processor: 24 GenuineIntel 13th Gen Intel(R) Core(TM) i7-13700K [Family 6 Model 183 Stepping 1]
23-Mar-2023 17:08:27 [---] Processor features: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush acpi mmx fxsr sse sse2 ss htt tm pni ssse3 fma cx16 sse4_1 sse4_2 movebe popcnt aes f16c rdrandsyscall nx lm avx avx2 tm2 pbe fsgsbase bmi1 smep bmi2
23-Mar-2023 17:08:27 [---] OS: Microsoft Windows 11: Professional x64 Edition, (10.00.22621.00)
23-Mar-2023 17:08:27 [---] Memory: 31.67 GB physical, 40.67 GB virtual
23-Mar-2023 17:08:27 [---] Disk: 464.49 GB total, 78.68 GB free
23-Mar-2023 17:08:27 [---] Local time is UTC -7 hours
23-Mar-2023 17:08:27 [---] WSL detected:
23-Mar-2023 17:08:27 [---] [docker-desktop-data] (default): <3>WSL (29) ERROR: CreateProcessEntryCommon:368: getpwuid(0) failed 2
<3>WSL (29) ERROR: CreateProcessEntryCommon:372: getpwuid(0) failed 2
<3>WSL (29) ERROR: CreateProcessEntryCommon:574: execvpe /bin/sh failed 2
<3>WSL (29) ERROR: CreateProcessEntryCommon:583: Create process not expected to return (<3>WSL (23) ERROR: CreateProcessEntryCommon:368: getpwuid(0) failed 2 [<3>WSL (32) ERROR: CreateProcessEntryCommon:368: getpwuid(0) failed 2
<3>WSL (32) ERROR: CreateProcessEntryCommon:372: getpwuid(0) failed 2
<3>WSL (32) ERROR: CreateProcessEntryCommon:574: execvpe /bin/sh failed 2
<3>WSL (32) ERROR: CreateProcessEntryCommon:583: Create process not expected to return])
23-Mar-2023 17:08:27 [---] [docker-desktop]: Linux (Docker Desktop [5.15.90.1-microsoft-standard-WSL2])
23-Mar-2023 17:08:27 [---] VirtualBox version: 7.0.6
23-Mar-2023 17:08:27 [SiDock@home] General prefs: from SiDock@home (last modified 10-Mar-2023 08:25:55)
23-Mar-2023 17:08:27 [SiDock@home] Host location: none
23-Mar-2023 17:08:27 [SiDock@home] General prefs: using your defaults
23-Mar-2023 17:08:27 [---] Reading preferences override file
23-Mar-2023 17:08:27 [---] Preferences:
23-Mar-2023 17:08:27 [---] max memory usage when active: 16215.46 MB
23-Mar-2023 17:08:27 [---] max memory usage when idle: 29187.84 MB
23-Mar-2023 17:08:27 [---] max disk usage: 79.82 GB
23-Mar-2023 17:08:27 [---] max CPUs used: 15
23-Mar-2023 17:08:27 [---] suspend work if non-BOINC CPU load exceeds 25%
23-Mar-2023 17:08:27 [---] (to change preferences, visit a project web site or select Preferences in the Manager)
23-Mar-2023 17:08:27 [---] Setting up project and slot directories
23-Mar-2023 17:08:27 [---] Checking active tasks
23-Mar-2023 17:08:27 [Einstein@Home] URL https://einstein.phys.uwm.edu/; Computer ID 13127743; resource share 100
23-Mar-2023 17:08:27 [Einstein@Home] Not using CPU: project preferences
23-Mar-2023 17:08:27 [Einstein@Home] Not using Intel GPU: project preferences
23-Mar-2023 17:08:27 [SiDock@home] URL https://www.sidock.si/sidock/; Computer ID 46785; resource share 1
23-Mar-2023 17:08:27 [World Community Grid] URL http://www.worldcommunitygrid.org/; Computer ID 8696965; resource share 100
23-Mar-2023 17:08:27 [World Community Grid] Not using AMD/ATI GPU: project preferences
23-Mar-2023 17:08:27 [World Community Grid] Not using Intel GPU: project preferences
23-Mar-2023 17:08:27 [---] Setting up GUI RPC socket
23-Mar-2023 17:08:27 [---] Checking presence of 522 project files
23-Mar-2023 17:08:27 Initialization completed
23-Mar-2023 17:08:27 [---] Suspending computation - user request
23-Mar-2023 17:08:27 [World Community Grid] Started upload of MCM1_0197252_8279_1_r131177174_0
23-Mar-2023 17:08:27 [World Community Grid] Started upload of MCM1_0197252_8183_0_r1633197180_0
23-Mar-2023 17:08:27 [World Community Grid] Sending scheduler request: Requested by project.
23-Mar-2023 17:08:27 [World Community Grid] Reporting 6 completed tasks
23-Mar-2023 17:08:27 [World Community Grid] Not requesting tasks: too many uploads in progress
23-Mar-2023 17:08:28 [World Community Grid] Error reported by file upload server: Server is out of disk space
23-Mar-2023 17:08:28 [World Community Grid] Error reported by file upload server: Server is out of disk space
23-Mar-2023 17:08:28 [World Community Grid] Temporarily failed upload of MCM1_0197252_8279_1_r131177174_0: transient upload error
23-Mar-2023 17:08:28 [World Community Grid] Backing off 05:29:33 on upload of MCM1_0197252_8279_1_r131177174_0
23-Mar-2023 17:08:28 [World Community Grid] Temporarily failed upload of MCM1_0197252_8183_0_r1633197180_0: transient upload error
23-Mar-2023 17:08:28 [World Community Grid] Backing off 05:12:00 on upload of MCM1_0197252_8183_0_r1633197180_0
23-Mar-2023 17:08:28 [World Community Grid] Started upload of MCM1_0197239_2098_1_r254159007_0
23-Mar-2023 17:08:28 [World Community Grid] Started upload of MCM1_0197239_1947_0_r625512618_0
23-Mar-2023 17:08:28 [World Community Grid] Scheduler request completed
23-Mar-2023 17:08:28 [World Community Grid] Server error: feeder not running
23-Mar-2023 17:08:29 [World Community Grid] Error reported by file upload server: Server is out of disk space
23-Mar-2023 17:08:29 [World Community Grid] Error reported by file upload server: can't open file
23-Mar-2023 17:08:29 [World Community Grid] Temporarily failed upload of MCM1_0197239_2098_1_r254159007_0: transient upload error
23-Mar-2023 17:08:29 [World Community Grid] Backing off 04:04:32 on upload of MCM1_0197239_2098_1_r254159007_0
23-Mar-2023 17:08:29 [World Community Grid] Temporarily failed upload of MCM1_0197239_1947_0_r625512618_0: transient upload error
23-Mar-2023 17:08:29 [World Community Grid] Backing off 03:19:19 on upload of MCM1_0197239_1947_0_r625512618_0
23-Mar-2023 17:08:30 [---] Suspending GPU computation - user request
23-Mar-2023 17:08:31 [---] Resuming GPU computation
23-Mar-2023 17:08:34 [Einstein@Home] Sending scheduler request: To report completed tasks.
23-Mar-2023 17:08:34 [Einstein@Home] Reporting 3 completed tasks
23-Mar-2023 17:08:34 [Einstein@Home] Not requesting tasks: don't need (CPU: ; AMD/ATI GPU: job cache full; Intel GPU: )
23-Mar-2023 17:08:36 [Einstein@Home] Scheduler request completed
23-Mar-2023 17:08:36 [Einstein@Home] Project requested delay of 60 seconds
23-Mar-2023 17:12:10 [Einstein@Home] Computation for task h1_0090.80_O3aC01Cl1In0__O3MDFC1_CasA_91.00Hz_31_0 finished
23-Mar-2023 17:12:10 [Einstein@Home] Starting task h1_0090.80_O3aC01Cl1In0__O3MDFC1_CasA_91.00Hz_39_0
23-Mar-2023 17:12:12 [Einstein@Home] Started upload of h1_0090.80_O3aC01Cl1In0__O3MDFC1_CasA_91.00Hz_31_0_0
23-Mar-2023 17:12:12 [Einstein@Home] Started upload of h1_0090.80_O3aC01Cl1In0__O3MDFC1_CasA_91.00Hz_31_0_1
23-Mar-2023 17:12:14 [Einstein@Home] Finished upload of h1_0090.80_O3aC01Cl1In0__O3MDFC1_CasA_91.00Hz_31_0_1
23-Mar-2023 17:12:17 [Einstein@Home] Finished upload of h1_0090.80_O3aC01Cl1In0__O3MDFC1_CasA_91.00Hz_31_0_0
-------------------------------------------------------

Note the logs about WSL. Perhaps Boinc should have some sort of timeout if WSL command fails to respond? Or at least better logging...

Yes we can turn on better logging, but for that we need to increase your output file via cc_config.xml because with the logging function on the default 2MB is filled almost instantly. I'm sure if need be we can do that. But I don't think it's needed. Your startup log shows enough: your BOINC client is stuck in a boot loop, apparently crashing before getting through the whole loop, and restarting. This is why BOINC Manager cannot connect to the BOINC client, because, well, there is no BOINC client to connect to because it has crashed. I think due to the stuck WSL process taking up all CPU cores.

Seeing as how you fixed the problematic WSL startup process, we could think that fixed it.
My advice is to retry to reproduce it now, with the fixed WSL startup process, and see if you can do it again.

If not, it's down to that and doesn't really need an additional fix at this time.
If you can reproduce it now, we can think of adding a delayed startup of the BOINC Client & Manager.

Yes we can turn on better logging, but for that we need to increase your output file via cc_config.xml because with the logging function on the default 2MB is filled almost instantly. I'm sure if need be we can do that. But I don't think it's needed. Your startup log shows enough: your BOINC client is stuck in a boot loop, apparently crashing before getting through the whole loop, and restarting. This is why BOINC Manager cannot connect to the BOINC client, because, well, there is no BOINC client to connect to because it has crashed. I think due to the stuck WSL process taking up all CPU cores.

Seeing as how you fixed the problematic WSL startup process, we could think that fixed it.
My advice is to retry to reproduce it now, with the fixed WSL startup process, and see if you can do it again.

If not, it's down to that and doesn't really need an additional fix at this time.
If you can reproduce it now, we can think of adding a delayed startup of the BOINC Client & Manager.

Why does Boinc need WSL?
Also, does Boinc log anything before/during/after using WSL?

BOINC doesn't "need" WSL.

Some projects concentrate on particular operating system, for some or all of their research programs. If you have WSL installed and active, you can participate in projects that only have native applications for Linux. Without it, you can only be of use to projects which have native Windows applications. The choice is up to you.

Open cc_config.xml
Change <dont_use_wsl>0</dont_use_wsl> to <dont_use_wsl>1</dont_use_wsl>
If there is no <dont_use_wsl> entry you need to change logging options from boincmgr and cc_config.xml will be populated with default options.
I only heard about one wsl test on gpugrid. Nothing came out of it.

Open cc_config.xml
Change <dont_use_wsl>0</dont_use_wsl> to <dont_use_wsl>1</dont_use_wsl>
If there is no <dont_use_wsl> entry you need to change logging options from boincmgr and cc_config.xml will be populated with default options.
I only heard about one wsl test on gpugrid. Nothing came out of it.

Where is cc_config.xml? Everytime Boinc starts, in the log it says it cannot find it.

Resides in the same place as ever, have a look at your earlier post:
https://boinc.berkeley.edu/dev/forum_thread.php?id=14942&postid=111396

Where is cc_config.xml? Everytime Boinc starts, in the log it says it cannot find it.

Which is a totally normal startup message. It informs you there is no cc_config.xml file. One isn't necessary for BOINC to use or start. It's mostly used for adding debug flags, and use advanced preferences, such as larger output files and settings for usage of GPUs.

So, for a clean installed BOINC, there is no cc_config.xml file and BOINC informs you about it. Just as it informs me of:
01/04/2023 15:16:47 | | No WSL found.