'I have tried to recover my whole backup to an external HDD. It has failed three times with the error
"The operation failed because of a protection agent failure. Retry the operation (0x003E6)"
I have retried the recovery three times now.
The first failed after transferring ~51GB, the second after ~10MB and the third after 49GB. The external HDD certainly has enough room on the drive, it's a blank 1TB.
I have been able to recover a selection of folders in the past, this is the first time trying my whole backup.