I am just going to throw something to you, because I wonder if this is what the client shows.
Recently, we had an issue on the server I play on, similiar to this problem. The server was showing up on the list, it allowed for "connection" from clients, but after some 30 seconds, we were greeted with the text "Server is still initializing, please try again in a minute"...
The owner found out that it would be halting itself, and shuttig down, after being rebooted. even manual reboot was a failure. He ended up having to perform a rollback to an older backup, which ofcourse was annoying AF, but since it fixed the problem, we ended up not caring about it.
I added a screenshot that someone else provided to our discord. just for reference
And for OP. When you make posts like this, please remember to include more information than just "it was working fine, now nobody can join". The more information you supply to the community, the faster you can get an answer. I only say this, because I saw your post not 10 minutes after posting, but didnt feel the urge to supply any feedback, since there could be a million reasons to your problem, with an equal amount of troubleshooting and suggestions for a fix. I hope you understand