Hyper V backup issue on Ahsay OBM

After months of hassle free backups, we have this issue:

Unable to generate delta using CBT., Reason = "[QueryRCTChanges][QueryChangesVirtualDisk] path= “Virtual-disk.VHDX”, Error There is no change tracking data available associated with the specified change tracking identifier.rn"

Not sure if this is restricted to Hyper V or VMware.