Backup fails with "Storage vMotion detected" message.
In one particular case it was a 4 disk VM with disks stored on 4 separate datastores. Disks have same names. Ranger successfully backs up 3 first disks but then fails on 4th with error above.
Investigation (including mob search) did not reveal anything unusual about 4th disk and VM in general.
Restarting ESX/VC management services, re-registering VM did not help.
Attach another disk of the same size as 4th one.
Transfer all data from 4th disk to 5th, then detach the 4th disk from VM and delete from the datastore.
Backup job successfully completes with 4 var files created.