Over 40 clients in the same network, one of them refuses to connect?

I have over 40 clients working flawlessly in the network, but one of them refuses to connect. I’m using the exact same settings on all of them, all running on latest Windows 11 machines. Other clients show “Connected to local UrBackup server”, but this one is stuck on “Connected to internet server”. I’ve tried re-installing the client, migrating the settings from one machine to another, but nothing seems to work. Any ideas?