I seem to have a similar issue recently. My unraid server is just a data server and doesn't run 24/7, no vm nor docker but it randomly lock up and screen goes black. My system is just using intel IGP too from Pentium G4560 cpu. It was perfectly running fine when I ran it for days last March when I added 2 drives which from the time table it was at UnRaid 6.8.3. I haven't tried running 6.9.2 for long hours until last week that I start to notice the freeze on the system. I thought might be bad RAM but my memtest is all fine and I couldn't find any notable errors on syslog either. And I can't complete a 4 parity checks without freezing my server. Atm trying 6.9.2 on safe mode if I can finish the parity check. After this I will try to rollback to 6.8.3