We'll look into it. We've made some fixes these past few days, and that might be the cause. I'll include some relevant posts for anyone else that is looking into this from other instances.
Another post about piefed.ca: https://piefed.ca/c/main/p/640008/federation-issues-again
The recent changes we made: https://lemmy.ca/post/62827614
Similar issues from 4 weeks ago: