@nebulon I thought it was perhaps the Broken Links Checker on one of my WordPress installs, as as @marcusquinn noted it's widely known to sometimes cause such issues, but I've disabled that and I'm still getting these /mysql was restarted (OOM) (although they don't seem to appear in the event log?).
I note that the most recent one happened 5 minutes after my backups are due to start, and the other previous two times it's been 7-9mins before updates are due to run.
I wonder if either of those (backup/ update) processes might have something to do with it?
I guess I could just give mysql more memory and not worry, but be nice to know what's happening and why...