@feld @lain At this point I think I can confirm that RAM was the issue, as I have not seen this recur since I bumped the VM up to 2GB from 1GB.

This does make my leading theory (though not with anything approaching absolute certainty) that the current version of #Pleroma is more demanding in this regard than the ancient version I was on, because this certainly never was an issue before my upgrade.

It's possible that increased Fediverse traffic is to blame instead, but it was several months into this latest surge that I performed this upgrade, so the second-place suspect for me is just Ubuntu itself. I upgraded to Ubuntu Server 22.04 before upgrading Pleroma and didn't observe any problems until the Pleroma upgrade (at which point they started occurring within the hour at the time), but that could certainly have been just a(n un)lucky coincidence.