Yeah, this is specifically on sh.itjust.works for those viewing this thread elsewhere, but I'm sure other instances are struggling too. I'm not even seeing 500s, just a generic Firefox "Cannot complete request" on mobile and connection resets on Jerboa.
Edit: ah, yep, here come the 500s mixed in there as well.
This is gonna get quickly out of hand... there should have been an announcement that you should NOT join the most popular instances and just scroll down the list to join an instance that is preferably at the very bottom of the list.