Okay, so we got the alarm about excessive snapshot size and deleted snapshots.
It came back a while later and said "Unable to access file <unspecified filename> since it is locked"
Looking a little more closely, the snapshot was from commvault and it hadn't "Released disk lease" yet.
The end result is we still have a snapshot, which you can tell from the files in the VM's folder in the datastore, but snapshot manager shows no snapshots.
FIX:
Take a snapshot manually.
It will take a minute or so extra, but in the end it shows not only the one you created, but also the "Consolidate Helper- 0" snapshot
