Items to back up: Nothing shown under Disks/Volumes

Daily backup failed overnight, no information in logs other than "failed"

Looked at backup plan, under "Items to back up..." it shows "Disks/volumes" as expected, but instead of the C drive on the computer it shows "Resolving..." forever

Tried creating a new backup plan, selecting "Disks/volumes" for "Data to back up", but there are no drives listed under the computer name. The drives are listed if I select "Files" instead of "Disks/volumes".

Any ideas?
MV

P.S. Windows 8.1, Version 11.5 Update 6, build 11.5.43994