Some ESXi hosts can see and access virtual machine files in a set of NFS datastores. From another subset of hosts, these same datstores appear in vSphere client and you can select "Browse Datastore", but the VM files do not appear. The problem subset of hosts all began having this problem at the same time.
Within ESXi, at the command line you can cd to the directory that pertains to the datastore, but an ls command will not list the contents.
The problem is only on SOME datastores on the storage system, and only on SOME ESXi servers in the environment.
What could cause this?
Could there be any difference on the NFS server to how the access control is configured? Only some IP addresses or host names perhaps? Or some difference in the NFS export settings - no_root_squash?
What kind of NFS server are you using? What happened around the time this problem appeared?
If the files exist in the directory and each host has network access to the NFS server, it may be that the files' attributes changed and they're no longer visible to certain hosts. Try to list the hidden files in the datastore with ls -a. You can also try uploading a test file to the datastore from one of the affected hosts to see if you can access it. This can give some clues as to which files it affects or perhaps the permissions on the entire export.