Unable to Delete or Online Snaplock DP Volumes

• A 7-mode Snapmirror relationship was transitioned from 7-mode to ONTAP 9 using a TDP relationship type, for example using 7mtt.
• A XDP based Snapmirror update after the TDP relationship was aleady transitioned / broken-off, aborts with space error on DP volume side (both cDOT already):

Failed to create Snapshot copy snapmirror.<...> Additional space required: 1.80GB. (No space left on device)

• After an unclear chain of events, including unexpected node reboots source side and ONTAP updates destination side, the affected Snaplock Enterprise DP volumes remain offline with an alert during node startup:

Wed Oct 18 22:12:43+0200 [node:vv_apply_special04:wafl_online_mode_corrupted_1:alert]: params:{'type':'volume','vol':'MyVolume_dp'}

• Resizing the DP volume to mitiagte the No space left error, fails with:

Error: volsize: Error setting size of volume "MyVolume_dp". Unable to set volume attribute "size" for volume "MyVolume_dp" on Vserver "MyVserver". Reason: Volume has the fixed filesystem size option set.

• A Snapmirror break operation fails with an error that is misleading, because no 7-mode-Volumes nor even 7-mode-Snapshots are expected to exist anymore at this time after TDP was broken off already:

::> snapmirror break -destination-path myVserver:MyVolume_dp
Error: Snapshot copy "SomeSnapshot" is a 7-Mode Snapshot copy. Using a 7-Mode Snapshot copy is not supported by this operation.

Note: listing snapshots in this state is not possible, because the volume is offline.

• The nodeshell based volume status returns unexpected Volinfo mode and a state of offline and inconsistent:

::*> node run -node MyCluster-02 vol status -v MyVolume
       Volume   State           Status                Options
       MyVolume offline         raid_dp, flex         schedsnapname=ordinal, nbu_archival_snap=off,
                                cluster               batched_free_log_cap=, space_slo=none(disabled),
                                fast zeroed           zombie_reclamation_priority=urgent
                                wafl inconsistent
                                64-bit
...
                        Volinfo mode: 7-mode
...

• To online the affected volume fails with:

::*> volume online -vserver MyVserver -volume MyVolume_dp
vol online: Error onlining volume "MyVserver:MyVolume_dp". Unable to set volume attributes for volume "MyVolume_dp" on Vserver "MyVserver". Reason: The mode bits that
represent whether this volume is a 7-mode volume or a cluster-mode volume are inconsistent.

• Deleting the affected volume fails with:

::*> vol delete -vserver MyVserver -volume MyVolume_dp

Warning: Are you sure you want to delete volume "MyVolume_dp" in Vserver "MyVserver" ? {y|n}: y
[Job 5760] Job is queued: Delete MyVolume_dp.

Error: command failed: [Job 1337] Job failed: Failed to delete volume "MyVolume_dp" on Vserver "MyVserver". Reason: volume cannot be destroyed because it contains unexpired WORM files
       OR it contains files under legal hold OR it contains unexpired WORM snapshots OR it is an unexpired SnapLock Enterprise audit log volume OR the volume must be made online in order to
       permit a pending WAFL scan to complete. Make the volume state online and run 'volume snaplock show' command in order to get the expiration dates and the status of the scans