Something wrong with the federation? The subscriber count for different communities also seem a whole lot lower here than on other Lemmy instances. https://lemmy.sdf.org/communities/listing_type/All/page/1 for example states that !Lemmy.world@lemmy.world only has 83 subscribers.

I had the same issue earlier. Sometimes it got fixed by waiting but I also had success with unsubscribing (you need to be in the sidebar of the community) and subscribing again.

One theory based on some testing over at https://lemmy.world/c/test_community@sopuli.xyz - post with undefined language get stuck somewhere. Works fine when I set the language to Finnish or English.