I just upgraded a client to 11.5, and none of the backups worked!
After a bit of debugging, I figured out that the problem is that the path to the catalog and the members all contain the bullet (option-8) in the path.
I moved the sets, updated the sets in the retro console, and it seems to work now.
This was an upgrade from 10.5 to 11.5. This was working fine in 10.5, so the bug was introduced at 11.x version.