Hopefully it’ll mostly resolve given time. Just like when there was a mass exodus to mastodon, the major thrediverse servers are getting overloaded. This creates delays and it seems even lost messages. From experience I’ve had messages from fedia.io take anywhere from 20-120 minutes to show up on my mastodon. As admins beef up their servers, but also as excitement tones down and there is less enthusiastic usage, hopefully the problem will resolve for the most part.
I’m not sure what causes messages to be lost forever vs. just delayed. Maybe Kbin or Lemmy aren’t quite as robust in that? When mastodon was melting down, messages could take 8+ hours to get through, but they seemed to get through. I think your idea about a resync idea is a great one.
I posted on a two year old thread (not on the fediverse) this week. I found the thread by searching and I’m sure other people will too if they have the same problem. So why not?