hi and thanks everyone, the issue in topic seems solved and it was on my end: a DNS migration left citiverse.it with an AAAA record while nginx was still listening on IPv4 only, so IPv6-preferring instances couldn't reach me at all, Lemmy then flagged my server as dead and quietly stopped federating, with zero errors logged anywhere. Adding listen [::]:443 fixed it. Mentioning it only in case it saves someone else an afternoon.