There are functional firewall apps for android? Is Rethink good?

And the old settings that have been mysteriously switched back on…

Just one error in a full trst run with all 4 sticks? Maybe RAM voltage settings need some tweaking? I don’t know how common this is these days, but more RAM generally needed higher voltage to be stable. Usually any kind of RAM issues are pretty frequent though and too low voltage tends to fail at boot.

I have not been following PC hardware for a while, but there was a time when RAM slots and the sticks themselves were designed to be used as a pair. Could be something like that?

Also since it’s occasional, could also be corrupted OS file, harddrive/SSD read issue or even a driver issue. Have you looked what errors are in the event log with the BSODs? Is it same or similar each time or completely random?