I made a new account on a different instance and tried to subscribe to this community on the new account, but it just says 'Pending' rather than joined. It's not clear from the app what is pending. Or how long it should take
I have found that by brute force hitting the button between Subscribe and Pending enough it eventually switches to "Joined". I'm not proud of my troubleshooting method.
The brute force is strong with this one. I have seen the power of this technique. But if it doesn't work after 2 or 3 times I generally chill out and try again later, no use queuing up 1.5 million subscribe/unsubscribe messages if the instance hosting the community is legit broken for a while.
It seems more concerning that it is a symptom of federation failure. It may get you the local messages, but it also is a sign of how data is not flowing reliably between your local Lemmy instance and the remote instance that is hosting the community. If you are the first one to join a community, it may not have registered with the remote - and posts/comments may not be flowing.
Of greater concern is that if small updates like this aren't making it between Lemmy instances, how many comments are missing? Set Github bug on evidence of missing comments: https://github.com/LemmyNet/lemmy/issues/3101
Curious on that one as well, just set up an instance the other day and trying to seed it with some communities of interest and though I'm seeing the content a lot of them still show as pending. I'm wondering if this is similar to the oddity I've seen on Mastodon with relays that somehow don't get the notice that they've been accepted but still start getting the feeds.