Yeah and 92 posts from a single community (for the 2nd one, updated more recently) does seem excessive, but then again there has been a HUGE flurry of daily posts there (https://lemmy.world/c/tenforward) these last few days so... actually fairly believable. Especially if edits to a posts' content count towards that stat (I have no idea, just throwing that out there:-).
Though it is also strange that the 1st community is shown as having been updated a few hours ago. Except... those don't show up, at [email protected]? So maybe those updates are for comments/votes for the older posts, while somehow the newer posts are being slurped into the 2nd community, which then hides them from the end-user's view.
Anyway I don't know how to take this further to diagnose, but I hoped that bringing it to your attention could be of at least some use!:-)
I'm not sure what you mean by the latter - b/c in this case the community definitely exists, so "creating" it if the ID were to ever not be found would lead to... well, it could have lead to exactly something like this, actually? Also, would you really want to pull in posts from a community that doesn't already exist on a PieFed instance? Why even, especially if nobody has asked for it? So maybe instead of find_or_create, just a find_or_ignore?
But I have zero experience with ActivityPub, federation, or even much threaded-style programming, so I will leave such to you experts to puzzle out the actual solution!:-)