The "VSS Diff failed (An error occurred during the fast difference check; a slower method will be used instead)" issue has occurred.
This issue is usually caused by the shadow storage size being too small.
Use the command line and run the following command to resize the shadow storage:
X represents the disk letter (it is recommended to perform this operation on all accessible disks).
After making the changes, run the backup task again. If it still fails, contact our technical support by submitting a request.
Delete all shadow copies using the following two additional command line commands:
Run the backup again. If it still fails, contact our technical support by submitting a request.
vssadmin resize shadowstorage /for=X: /on=X: /maxsize=320MBvssadmin resize shadowstorage /for=X: /on=X: /maxsize=30%diskshadowdelete shadows all