App-aware backup fails after upgrade to 13.1 - for a few vms

[DanielJ]

Ticket: 08203921

After we upgraded from 12.3 to 13.1 a few servers are failing their app-aware backup because VBR can no longer connect to their admin shares. Only that it can - when testing the connection. When running the job, it fails. And this only affects a few servers, the large majority still works as usual even though we have never requested port 6173 (that now seems required) to be opened. My question that support is unable to answer is: all port changes aside, how is it possible that these servers pass the admin share test when testing the connection, but fail when the job is running?