About three days ago, I started experiencing this. Nothing in the event log seems to explain it. The computer is running with nothing else running apart from the OS, xfce and the gridcoin wallet. Tasks will run for about an hour or so and then the manager will say at bottom right that I am disconnected and system monitor shows the manager but not the client running. Restarting the client from a terminal gives the following output when the client fails.

22-Feb-2018 18:41:39 [---] GUI RPC bind to port 31416 failed: 98
22-Feb-2018 18:41:40 gstate.init() failed

Nothing has changed in setup of the computer since upgrading to 7.8.3 and this had run happily for some weeks since then. I tried suspending project number fields which had been running on its own and either running amicable numbers or WCG but this made no difference. It is currently running on 75% 3 cores to see if this makes a difference. Doubtless there is something obvious more I should be including but I can't for the life of me think what it is.
Event log

Thu 22 Feb 2018 19:19:02 GMT | | Starting BOINC client version 7.8.3 for x86_64-pc-linux-gnu
Thu 22 Feb 2018 19:19:02 GMT | | log flags: file_xfer, sched_ops, task, checkpoint_debug, file_xfer_debug
Thu 22 Feb 2018 19:19:02 GMT | | log flags: http_debug
Thu 22 Feb 2018 19:19:02 GMT | | Libraries: libcurl/7.55.1 OpenSSL/1.0.2g zlib/1.2.11 libidn2/2.0.2 libpsl/0.18.0 (+libidn2/2.0.2) librtmp/2.3
Thu 22 Feb 2018 19:19:02 GMT | | Data directory: /var/lib/boinc-client
Thu 22 Feb 2018 19:19:03 GMT | | No usable GPUs found
Thu 22 Feb 2018 19:19:03 GMT | | Host name: linux-laptop
Thu 22 Feb 2018 19:19:03 GMT | | Processor: 4 GenuineIntel Intel(R) Pentium(R) CPU N3540 @ 2.16GHz [Family 6 Model 55 Stepping 8]
Thu 22 Feb 2018 19:19:03 GMT | | 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 rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology tsc_reliable nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 movbe popcnt tsc_deadline_timer rdrand lahf_lm 3dnowprefetch epb pti tpr_shadow vnmi flexpriority ept vpid tsc_adjust smep erms dtherm ida arat
Thu 22 Feb 2018 19:19:03 GMT | | OS: Linux Ubuntu: Ubuntu 17.10 [4.13.0-32-generic]
Thu 22 Feb 2018 19:19:03 GMT | | Memory: 7.67 GB physical, 37.25 GB virtual
Thu 22 Feb 2018 19:19:03 GMT | | Disk: 72.87 GB total, 62.24 GB free
Thu 22 Feb 2018 19:19:03 GMT | | Local time is UTC +0 hours
Thu 22 Feb 2018 19:19:03 GMT | | Config: GUI RPCs allowed from:
Thu 22 Feb 2018 19:19:03 GMT | Amicable Numbers | URL https://sech.me/boinc/Amicable/; Computer ID 12520; resource share 100
Thu 22 Feb 2018 19:19:03 GMT | climateprediction.net | URL http://climateprediction.net/; Computer ID 1430655; resource share 200
Thu 22 Feb 2018 19:19:03 GMT | cpdnboinc_dev | URL https://vorvadoss.oerc.ox.ac.uk/cpdnboinc_dev/; Computer ID 660; resource share 600
Thu 22 Feb 2018 19:19:03 GMT | NumberFields@home | URL http://numberfields.asu.edu/NumberFields/; Computer ID 63203; resource share 100
Thu 22 Feb 2018 19:19:03 GMT | World Community Grid | URL http://www.worldcommunitygrid.org/; Computer ID 4081453; resource share 100
Thu 22 Feb 2018 19:19:03 GMT | | General prefs: from https://grcpool.com/ (last modified ---)
Thu 22 Feb 2018 19:19:03 GMT | | Host location: none
Thu 22 Feb 2018 19:19:03 GMT | | General prefs: using your defaults
Thu 22 Feb 2018 19:19:03 GMT | | Reading preferences override file
Thu 22 Feb 2018 19:19:03 GMT | | Preferences:
Thu 22 Feb 2018 19:19:03 GMT | | max memory usage when active: 7071.87 MB
Thu 22 Feb 2018 19:19:03 GMT | | max memory usage when idle: 7071.87 MB
Thu 22 Feb 2018 19:19:03 GMT | | max disk usage: 57.50 GB
Thu 22 Feb 2018 19:19:03 GMT | | don't use GPU while active
Thu 22 Feb 2018 19:19:03 GMT | | (to change preferences, visit a project web site or select Preferences in the Manager)
Thu 22 Feb 2018 19:19:03 GMT | | Using account manager grcpool.com
Thu 22 Feb 2018 19:19:03 GMT | | gui_rpc_auth.cfg is empty - no GUI RPC password protection

Edit: Now just running WCG and am trying without the Gridcoinc wallet running to see what happens.

An hour of running without the wallet running as well and no crash. Now restarted the wallet and about 10 minutes in without problems. Have also checked temps with psensors and all OK.