You may want to open a case to get some attention on this, but as a first step, I'd use the hidden ls command from the ONTAP CLI and see if the controller sees it. That should tell you if the data exists there and you're dealing with some kind of NFS issue (which would be my first educated guess).
netapp> priv set advanced
netapp*> ls /vol/<vol_name>/.snapshot/sv_nightly.6
When you're done:
netapp*> priv set