No valid data returned (No Such Instance currently exists at

[nagiosmagic]

I hope some experts here can outline some steps I can troubleshoot the cause of the issue.

We are using Nagios to monitor NetApp storage, and if the size of the volume is getting, an alert via email would be sent out.
All the sudden we have started to receive A LOT of messages such as:
No valid data returned (No Such Instance currently exists at this OID)
Check name: disk_netapp_/vol/volume_name@storage_name

Alerts like these seem invalid, and almost thousands a day, also not on all volumes. I am not familiar with Nagios, and the Admin is not available. On the storage side, i can see SNMP is enabled and nothing is changed. There are very limited a few things need to be done on the storage.

Can you please point out a few things I can try to perform to figure out the root case? Also, do I have to download MIB onto the Nagios management host?

Thanks in advance for your help.