SNMPv3 slow responses & timeouts on NMC3 in APDU9967

[ashappell]

I have been running into a strange issue with my APDU9967 with NMC3 installed in them.  If I use SNMPv1 to poll the devices everything works fine (I have 6 of them configured this way). I have an additional 12 configured to use SNMPv3.  The ones running SNMPv3 are having reachability and timeout issues.  On our NMS I am seeing that the PDUs polled via SNMPv1 complete in less than 4 seconds, the devices polled via SNMPv3 take about 40+ seconds to complete, if they complete at all. In my NMS logs I am seeing all types of errors messages for the snmpv3 polled PDUs about unreachability, status changes from up to down then back to up. I am seeing the same responses when trying to do snmpwalks on the devices.  Any ideas or suggestions, I have hundreds of other devices configured to use SNMPv3 without issue, so it is not a NMS or Network issue.  Thanks..

NMC Model ON-1556

Rack PDU Firmware 1.2.0.2

APC OS Firmware 1.5.1.1

Boot Monitor Firmware 1.3.6.1