I posted over at SETI as there is a recent thread about this problem. Just started on a new 18.04 system I put together yesterday. I googled around and found several of the "postponed for 30 seconds" problems but no solutions seems to work and I probably need to enable some log flags to get more info about that is happening.

Ati drivers were installed from amdgpu-pro-19.10-785425-ubuntu-18.04.tar
using
sudo ./amdgpu-install --OpenCL=legacy

WCG tasks run fine but gpu tasks have problems:
all milkway error out (no 30 second stuff)
all setiathome run 2 seconds and generate that 30 second error message
[edit] - all seti tasks finally error'ed out, just took longer for them to think about it.
I would like to debug this but don't know what debug flags to set.
I have issued the command
boinccmd --set_gpu_mode always

where in cc_config.xml can I verify that the above worked?

This is the first Linux system I have built that uses those S9000 "pro" AMD cards.
I noticed that "amdgpu-pro-install" is just a link to amdgpu-install so there is no longer any specific "pro" driver from AMD for Linux unlike windows..

1			7/19/2019 12:00:16 PM	Starting BOINC client version 7.14.2 for x86_64-pc-linux-gnu	
2			7/19/2019 12:00:16 PM	log flags: file_xfer, sched_ops, task	
3			7/19/2019 12:00:16 PM	Libraries: libcurl/7.58.0 OpenSSL/1.1.1 zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1 (+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3	
4			7/19/2019 12:00:16 PM	Data directory: /var/lib/boinc-client	
5			7/19/2019 12:00:17 PM	OpenCL: AMD/ATI GPU 0: ATI FirePro V (FireGL V) Graphics Adapter (driver version 2841.4, device version OpenCL 1.2 AMD-APP (2841.4), 3072MB, 3072MB available, 1613 GFLOPS peak)	
6			7/19/2019 12:00:17 PM	OpenCL: AMD/ATI GPU 1: ATI FirePro V (FireGL V) Graphics Adapter (driver version 2841.4, device version OpenCL 1.2 AMD-APP (2841.4), 3072MB, 3072MB available, 1613 GFLOPS peak)	
7			7/19/2019 12:00:17 PM	OpenCL: AMD/ATI GPU 2: ATI FirePro V (FireGL V) Graphics Adapter (driver version 2841.4, device version OpenCL 1.2 AMD-APP (2841.4), 3072MB, 3072MB available, 1613 GFLOPS peak)	
8			7/19/2019 12:00:17 PM	[libc detection] gathered: 2.27, Ubuntu GLIBC 2.27-3ubuntu1	
9			7/19/2019 12:00:17 PM	Host name: jysdualxeon	
10			7/19/2019 12:00:17 PM	Processor: 24 GenuineIntel Intel(R) Xeon(R) CPU X5675 @ 3.07GHz [Family 6 Model 44 Stepping 2]	
11			7/19/2019 12:00:17 PM	Processor features: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmper	
12			7/19/2019 12:00:17 PM	OS: Linux Ubuntu: Ubuntu 18.04.2 LTS [4.18.0-25-generic|libc 2.27 (Ubuntu GLIBC 2.27-3ubuntu1)]	
13			7/19/2019 12:00:17 PM	Memory: 11.72 GB physical, 2.00 GB virtual	
14			7/19/2019 12:00:17 PM	Disk: 109.53 GB total, 95.54 GB free	
15			7/19/2019 12:00:17 PM	Local time is UTC -5 hours	
16			7/19/2019 12:00:17 PM	Config: GUI RPC allowed from any host	
17			7/19/2019 12:00:17 PM	Config: GUI RPCs allowed from:	
18			7/19/2019 12:00:17 PM	    jysarea51	
19			7/19/2019 12:00:17 PM	Config: use all coprocessors	
20	Milkyway@Home	7/19/2019 12:00:17 PM	URL http://milkyway.cs.rpi.edu/milkyway/; Computer ID 810090; resource share 100	
21	SETI@home	7/19/2019 12:00:17 PM	URL http://setiathome.berkeley.edu/; Computer ID 8772790; resource share 100	

and 100's of the following but no error'ed tasks except for milkyway

70	SETI@home	7/19/2019 12:01:51 PM	Task 17jl19ab.1022.17245.15.42.242.vlar_1 postponed for 30 seconds: 	
71	SETI@home	7/19/2019 12:01:52 PM	Task blc45_2bit_guppi_58642_03722_HIP55210_0016.25435.818.22.45.130.vlar_1 postponed for 30 seconds: 	
72	SETI@home	7/19/2019 12:01:53 PM	Task blc42_2bit_guppi_58642_03722_HIP55210_0016.26020.409.22.45.219.vlar_1 postponed for 30 seconds: 	
73	SETI@home	7/19/2019 12:01:54 PM	Task blc42_2bit_guppi_58642_03722_HIP55210_0016.26020.409.22.45.216.vlar_1 postponed for 30 seconds: 	
74	SETI@home	7/19/2019 12:01:55 PM	Task blc42_2bit_guppi_58642_04042_HIP55426_0017.26054.409.22.45.119.vlar_1 postponed for 30 seconds: 	
75	SETI@home	7/19/2019 12:01:56 PM	Task blc42_2bit_guppi_58642_04362_HIP55210_0018.26043.409.22.45.161.vlar_1 postponed for 30 seconds: 	
76	SETI@home	7/19/2019 12:01:57 PM	Task 17jl19ab.1022.17245.15.42.252.vlar_0 postponed for 30 seconds: 	

I asked over at the AMD community if the S9000 is supported in 18.04 as it is not clear from the release info. In any event, I will be returning the boards back to windows once I repair the motherboard caused by 18 awg wireing on an adapter.

I have ordered 16awg adapter wiring but I need to solder wires as the pins are not any good on the mombo and still need to verify the mombo (hp-z400) will work.