This time the issue was on the lemmy.world side where their federation worker responsible for lemmy.dbzer0.com, lemmy.blahaj.zone and lemmings.world among others b0rked and was sending 1 federation per minute at best. Unfortunately it seems just that single federation worker borked, which affected us again, because we're cursed apparently. Fortunately this meant that from our previous problems I had enough experience to know where to look. Unfortunately many people were thinking that existing issue along with some mbin spam was the problem, but it was a red herring in this case.
Anyway @ruud@lemmy.world restarted their federation workers and now we're catching up again. Will take like a day for that to happen.