Lemmy federation has been known to be buggy in certain releases before, and I really dont know what to do about it except try to keep up to date about bugs. I guess its a complex system underneath. From what ive read, its a queue of federation work that is supposed to take place, and stay in the queue until its successful. But I wish there was a good way to see the status of it.
I have been looking in db tables and log files before to figure out the current status and it works, but its not so convenient.