As a starting point of all or nearly all troubleshooting Nutanix recommends running Nutanix Cluster Checks (NCC). NCC identifies any risks or misses in the cluster configuration, hardware state, software components, networking and more.
Checking for presence of orphan VM snapshots is part of NCC which, I think is quite convenient as chasing orphaned snapshots can be a hassle.
Should you already know that there is a snapshot that is orphaned it can be removed with a single aCLI command. To be on the safe side always validate that the VM no longer exist. Otherwise, solution section of KB-3752 NCC Health Check: orphan_vm_snapshot_check lists all the steps necessary.
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