Please give this output:
From storage:
Try to access the share \\hostname\share, and then check event log.
::> event log show -message-name secd*
::> vserver cifs security show -vserver <vserver_name> -fields Lm-compatibility-level
::> vserver cifs show -vserver <vserver_name>
From WIN2K12:
C:\Users\user\admin>setspn -L host (CIFS Server NetBIOS Name)
You haven't mentioned the ONTAP version here. But, bydefault, all SMB versions are enabled (From 9.2, SMB1 can be disabled). Anyway, I think If you can access the share via IP, then it is something to do with DNS and auth-mechanism.