So, I made a post in a Lemmy group that I was using before moving to Piefed. I made it using my piefed account on piefed.ee.
It's now properly visible through lemmy.ee, but not visible on the actual instance where the group is located, nor on piefed.social. The image shows all three: piefed.ee first, then Sopuli, then piefed.social. As you can see, the topmost post is missing in the lower two screenshots.
I've tried refreshing Sopuli's view of the community and I've tried leaving the community and joining it. But, nothing.
It could be it has an effect that the "type" of post I chose on Piefed was "Link", because I wanted the post to include a link as is very common on Lemmy posts. But, that would be very weird, because it's indeed a type of post very common on Lemmy, so why would that be a problem when posted into a community on a Lemmy instance from within a Piefed instance?
Check the language. Your profile needs to be set to display posts in the same language as the post is set as.
See my other comment
I've got no languages selected, and the settings screen tells this equals selecting every language on the list.