Acronis True Image: unable to select a disk for new backup, already configured backups fail, if volsnap is missing from UpperFilters in the system registry

Symptom 1

Entire PC backup interrupts with message "Source is not selected. The operation has been terminated".

Symptom 2

After interruptions and retries, illustrated above, Entire PC backup transitions to the "failed state" and a red cross is displayed. The error text says "Source is not selected. The operation has been terminated".