The server will be down from 18:00 UTC for possibly one hour (not sure how long exactly) to replace the current docker + compose setup with an ansible setup. This is to hopefully fix any current federation problems, and if not, then to at least eliminate any issues software wise.
On a related note - If you're a technowizard, especially when it comes to ActivityPub and Lemmy BE, please message me (either here, over email, Discord (nullishcat), Matrix (nullishcat:matrix.org), or Divolt.) I still do not know the root cause of this problem and have nearly exhausted all potential fixes (the remaining ones being this setup change and switching providers.)
EDIT: We're back up, very sorry for the long wait. (Ansible's setup guide is very poor and didn't make it clear that it needs to be run on a local PC running Linux/Mac and to copy the volumes to /srv/lemmy/volumes.) Federation tests will start shortly.