ONTAP upgrade validation cannot start due to a volume in a MIXED state

• 9.12.1P3
• AFF-A300
• FlexGroup

• During the ONTAP upgrade validation step, the validation is showing:

Error: Validation could not be completed due to errors. Fix the errors, and validate again.

• EMS is showing:

Sat Jul 29 16:26:36 +0000 [node_name: mgwd: mgmtgwd.jobmgr.jobcomplete.failure:info]: Job "Vol Modify" [id 8889] (Modify NetApp_VOL) completed unsuccessfully:
The volume operation was successful but the state of the volume is "mixed"  because the FlexGroup volume has not finished updating. Wait a few minutes, and then
check that the state of the volume is "offline" using the "volume show -vserver <vserver_name> -volume NetApp_VOL -fields state" command. For further assistance
contact technical support. (13107231).

• However, when checking the vol show state, the volume is ONLINE:

::> vol show -vserver <vserver_name> -vol NetApp_VOL -fields state
vserver   volume     state      
--------  ---------  --------
svm1      NetApp_VOL  online

•   Also, the volume has a constituent in OFFLINE state and FlexGroup in UNHEALTHY status:

::> volume show -is-constituent true
Vserver   Volume                  Aggregate  State     Type  Size   Available  Used%      
--------  ----------------------  ---------  --------  ----  -----  ---------  -----
svm1      NetApp_VOL_CONSTITUENT  aggr_1     offline   RW    105GB          -      -

::> volume show 
Vserver   Volume                  Aggregate  State     Type  Size   Available  Used%      
--------  ----------------------  ---------  --------  ----  -----  ---------  -----
svm1      NetApp_VOL               -          online    RW    0B             0B  100%
svm1      NetApp_VOL_CONSTITUENT  aggr_1     offline   RW    105GB          -      -

::*> volume flexgroup show

Vserver:    svm1
FlexGroup:  NetApp_VOL
Node:       node1
 
Next VLDB update due (msec): 0
Next snapshot cleanup due (msec): 5485
Next refresh due (msec): 18446744073709551101
Last refresh member: 0x80D60EEA
Done VLDB update: true
Protocol version: 14.11
Protocol capability: 0x1FF7F
All member have assigned index: false
Ref count: 2
Quotas enforced: Unknown
Any member have NVFAILED state: false
Workflow: +0.0 (auto)
Reaction: +0.0     Activity: 0        Imbalance: 0%

                  Byte Rates_______________ Op Rates___________________________ Protocol_______________  
Index Status    DSID Read       Write       Read        Write       Metadata    Version     Capability
----- --------- ---- ---------- ----------- ----------- ----------- ----------- ----------- -----------
1     Unhealthy -    -          -           -           -           -           -           -          

• In this situation when trying to delete the constituent volume, the system shows an error (In this case the data in the volume was not needed nor the volume was needed either)

::> volume delete -vserver <vserver_name> -vol NetApp_VOL_CONSTITUENT
Error: command failed: Volume "NetApp_VOL" in Vserver "svm1" must be offline before constituent "NetApp_VOL_CONSTITUENT" can be  deleted.

• The error is saying that, to delete the constituent the volume needs to be offline first, however when trying to offline the volume, it is not possible due to the same MIXED state:

::> volume offline -vserver <vserver_name> -vol NetApp_VOL

Warning: Forcing offline volume SOFTWARE in Vserver SVM1 can potentially disrupt access to files in other volumes.
Do you want to continue? {y|n}: y
[Job 8889] Steps completed: 1 of 2.vol offline: Error offlining volume "svm1:NetApp_VOL". [Job 8889] Job failed: The volume operation
successful but the state of the volume is "mixed" because the FlexGroup volume has not finished updating. Wait a few minutes, and then
check that the state of the volume is "offline" using the "volume show -vserver <vserver_name> -volume NetApp_VOL -fields state" command.
For further assistance, contact technical support.