Please clarify stpe 3. Do you only see the LUN under "Storage Adapters", or do you see the datastore under "Storage", but it doesn't show data anymore?
In case you can see the LUN, but the datastore isn't mounted, follow the "Command Line" steps from https://kb.vmware.com/kb/1011387 (i.e. run esxcli storage vmfs snapshot list) to see whether the LUN has been detected as a Snapshot LUN, and can be mounted manually.
André