The cause is unclear to me, but the processes that manage incoming and outgoing federation were “stuck” until I manually intervened. It’s running now. I’m adding to my to-do list for after my job ends in 10 days to implement some sort of detection and hopefully automated restart for when this happens again.
That GitHub tracker is for problems with mbin code, not with instances running Mbin software. The problem that Fedia experienced is very likely caused by a bug of some sort in mbin (or something that Mbin is depending on), but we don’t know for sure what it is yet. Once I’m unemployed in a week, I hope to have more time to debug issues like this and get them resolved.