Do you have an active ticket with support on this?
In general, I've seen this when an API call fails. Usually, it's because you don't have a license activated for a particular feature on the NetApp Filer itself. For example, we may be querying for information owned by SnapMirror, but you don't have a SnapMirror license. Can you run a license check on your NetApp filer and post back the output? Your best bet is probably to open a ticket with Support though as troubleshooting this on Thwack may require a bit of back and forth.
This problem fixed itself after upgrading OnTap from 8.1.2 to 8.2.1P2.