As check result on any snmp sensor on the core-switch PRTG reports: Error opening snmp session: Unknown host (10.9.1.1:161) (SNMP error # -2006). Tried to run snmp tester from probe machine and it reports no result.
If not even the SNMP Tester is then able to "produce" a proper result, this really seems as if there is a serious issue on the underlying Windows. Maybe it would be good to (try to) move PRTG to a new host.
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