- Do all the snapshot's - to which you want to revert - associated *.vm* files exist in the VM's folder?
- Did the VM (the snapshot) have e.g. an ISO image attached to it, which doesn't exist anymore, or has been moved?
I have seen this an several VMs upgraded from v12. It's as if the upgrade removed the last snapshot disk files. Someone else in my group has also seen it.
It also happened when I simply reverted a working v15.5 VM to a previous snapshot. Out of the blue it can't find the files.
I'm vigilant in keeping my win10 filehistory up to date. I can't trust VMware any more.