The datastore summary says 0 hosts and there are no files seen in the DS. The ds was somehow removed from all of the hosts last week hence 0 Hosts.
If it was not manual then there could be something went wrong at the storage end, only logs can tell us what happened actually.
Do you know what was used space in the DS before the issue ? because now I see the datastore is almost empty. I only looked at the contents of the ds after the issue had occurred else had been working on it. However; I have a couple of assumptions: the path to a .vmx file listed under virtual machines in one of the hosts seems to indicate that our backup server stored its files on the ds. My other assumption (and I'm really just guessing here) is that some HA process migrated the files to this ds and then something went wrong.
HA wont migrate the files among datastore, it just restarts the VMs when ESXi goes down unexpectedly. You have to confirm by referring your old data (rvtools data/ inventory export) to confirm what was there in this datastore before this issue. guessings wont work out much ,sometimes VM data might be scattered across multiple datastores.
While adding the DS again, did you remove this Ds from inventory and added it again ? I did not. My assumption was that this was unnecessary because the ds was removed from the hosts.
Since this DS is not mounted on any ESXi hosts, the object is still in vCenter DB which shows in the inventory which is of no use. you may remove the datastore and try adding it again.
What is the error you see while adding this DS if it is failing our while adding it again. By adding are you referring to mounting?
Yes, mount this NFS again on ESXi as datastore, while trying to do that we will come to know the status of the mount, if it is still a healthy NFS mount then we will be able to add the datastore and read the data else it will error out.
The errors related to host system board and insufficient DS for HA are not related to this issue. However, we have to find what happened at the back end to the NFS export where we see no data in it.
Have a word with your storage team to know about the health status of this mount point and check What they see at storage end.