Here is a bizare one for you guys 
Just installed the lates Orion NPM 9.5 sp3 and running into an odd problem. The historical data is available for network interfaces but SNMP polling randomly stops for all objects (drives, cpu, memory). You can see real-time stats but no historical data. Also if you look in the polling stats the SNMP OUTSTANDING goes through the roof and SNMP statistics index shows 0 out of %number of polls%. The problem goes away after the server is rebooted or services restarted.
Its a Windows 2008 Server running on VMWare.
Tried disabling Anti-Virus
Windows firewall is off
CPU and RAM utilization appear to be normal
Any ideas?