Unable to monitor CPU utilization with NMIS 8.6.1G however it was monitoring with NMIS 8.5.8G. Please refer to below image and suggest.
You can also just use snmpwalk to see if the raw data is even being received, like this:
Even More: http://www.ietf.org/rfc/rfc1514.txt
Perhaps also NMIS has interpreted the wrong model, you can also check that the model is correct in Edit Node > Advanced Options > Model
When this happens to me I run the following commands, then look through the resulting files to determine if CPU information is being collected. Usually I'll find some clue as to what the problem is with this approach.