Long story short: I messed up with the domain registration for this instance, and never replied to a mandatory email. The domainname (lemmit.online) got put in suspension, causing disconnects all over the fediverse.

I fixed it as soon as I found out, but it will probably take a few more hours for the issues to be fully fixed.

So ehm. Whoops. Hope this explains and fixes the federation issues we've been having today.