The protocol they have in common is ActivityPub, the same thing used by Mastodon, Calckey, etc..

I think it's because of the server overload some instances have been suffering. It might be affecting sync between instances in addition to the timeouts for user interaction.

I'm on kbin, and to sub to a community on a lemmy instance, I have to replace the ! with a @, because that's the actual underlying name, it seems. It's a bit confusing.