It is not a Jerboa issue,
This community has never been active and that was the latest post in Jerboa in Lemmy instance.
You can query this directly and see.
https://lemmy.one/api/v3/post/list?type_=All&sort=New&community_id=49 https://lemmy.world/api/v3/post/list?type_=All&sort=New&community_id=91
Lemmy always had some federation issues its better now then before.
But you can still see some issues. For example
lemmy.world does not have the switching language on gboard.
post.
see https://lemmy.world/c/jerboa@lemmy.ml?dataType=Post&sort=New
As a test, I tried posts from /all/, and was quickly able to find one that is visible for me from /all/ but does not appear on its own community page under new - the post on politics@lemmy.world about a 271 page document on Vance (about an hour ago).
Did you check this within the same instance? /all/ and the community page?
I checked right now and I found the post you are talking about. So it is definitely visible right now. https://lemmy.world/post/18503617