We currently monitor 5 HP Proliant servers with the SNMP health sensor and have a strange problem. Sporadically, all of them will go "down" at the same time and say "No response (check: firewalls, routing, snmp settings of device, IPs, SNMP version, community, passwords etc) (SNMP error # -2003)". About 12 hours later, they all come back up again for no apparent reason. While this is happening, other SNMP sensors continue to work fine.
I find it hard to imagine all 5 servers are having an issue at the same exact time. It seems more likely that PRTG is having an issue during this time frame, but the issue doesn't effect other SNMP sensors at all, so I'm not sure what to make of it. Whenever this happens, it seems to start between 12:30 and 1:30 in the morning and always lasts about 12 hours.