After upgrading to ONTAP 9.4 (or later,) attempts to modify a volume's vserver-dr-protection property fail with "entry doesn't exist."

ONTAP 9.4 - ONTAP 9.7
One or more DP relationships being converted to SVM DR relationships
Some source volumes do not need to be replicated for DR, and are being excluded.

When converting Volume Replication relationships (DP relationships) to SVM DR relationships, it is necessary to modify un-needed volumes, setting them as unprotected.
If the un-needed volumes are not set as unprotected, the snapmirror resync required for converting to SVM DR will fail.
To mark un-needed volumes as unprotected, we use the vol modify command.
After upgrading to ONTAP 9.4, when vol modify is used to set a volume's vserver-dr-protection property to unprotected, the command fails with the message:

Error: command failed: Failed to modify the protection type of the volume [volume name.] Reason: entry doesn't exist.