I'm guessing all the shitposts that don't load on 196@blahaj for me are from users on overloaded instances, because when I post there, the image is uploaded to my home instance and referenced in that post on the 'foreign' instance. Plenty of error placeholders there lately. Concerning your question: I think a community gets delayed into your feed if its server federates slowly or not at all until it is up again. I see sudden post batches appear in my feed sometimes and unseen posts from hours ago.