So it's very simple, our backup server (infrastructure appliance) had a proxy server configured for access to Internet (in order to fetch updates etc.)
Everything good in 13.0.
In 13.1 it seems to be trying to use internet proxy to connect to anything http(s), even “localhost”. Goes without saying that Backup server doesn't even properly start (system services can't connect to local identity service bc that sends them to internet proxy).
After defining proxy exceptions for localhost etc., connections to data movers still fail, again because those connections attempt to go through internet proxy.
Case is open with support. Reverted to 13.0. Careful!
