I have found that Policy objects (which were introduced in SC 4.1) do not work for Restores in the SnapCreator GUI.
When choosing the Restore option I need to choose a Volume and a Policy to restore from. When I have a config with one of the default policies 'hourly, daily, weekly, monthly' I can choose it. But when I have a config that is attached to a Policy Object, I cannot choose any (dropdown is empty) and cannot proceed with the restore dialog.
I have checked once again also older releases (4.1 -> 4.1.1P4, fresh installation) and I was able to mount/umount and restore custom policy snapshots too... It's quite interesting that it's working now and was not working before - otherwise I would not write a post in this thread... 😉
I did not create a case because I thougt marcel_juhnke (creator of this thread) created one after marking this thread as solved.