Lemmy federation, server to server, is having a number of problems. Comments and postings aren’t always getting copied over to all the servers who have subscribers. For over a week, Lemmy.ml has had regular nginx 500 error codes on the front page, sometimes you have to refresh 3 or 4 times to get a page to load.

Growing pains.

When subscribing to communities it occasionally says “Subscribe Pending”

Your specific issue is documented and I opened a fresh issue on it today: https://github.com/LemmyNet/lemmy/issues/3203