Hi!
Got the same error today, basically triggered from Veeam, but related to taking snapshot of my VM, before backup.
Finding
I did a quick troubleshoot in the vmware.log of the affected VM, and found a locking issue, like this:
"2021-05-16T15:38:49.953Z| vmx| | W003: DISKLIB-CBT : ChangeTrackerESX_GetMirrorCopyProgress: Failed to copy mirror: Lost previously held disk lock".
Resolution/workaround
Since the locking is held locally by the host, I just did a vMotion of the VM (to another host, in my cluster), to re-issue the lock by another host. Re-trying snapshot, it now completed successfully (and backup is now working again).
