So recently I started monitoring a few Cisco WLC's using the template provided in the relevant kb post. Everything seemed to be working quite well at first. However, over last weekend the error "Could not find a table row matching the index you specified when adding the sensor" occurred about a 100 times. All sensors eventually returned to a normal state. I've encountered the same problem with the monitoring of the VPN tunnels of a checkpoint firewall using a custom snmp table. When I keep on rescanning the sensor manually, the error eventually goes away,.
The weird thing is that I also use around 150 sensors (snmp custom table) per F5 load balancer to monitor things like virtual servers, pool members etc. without experiencing the same error.
Some more info: License: PRTG Unlimited Sensors: 5100 Hardware: VM 16 GB Ram 8 CPU cores SNMP: V3
Scanning Interval WLC AP: 10 minutes Scanning Interval Firewall: 120s