High CPU Usage after Error in logs

We had an issue where gateway CPU usage rose dramatically as pictured. This rise corresponds with this error in the gateway wrapper log:

INFO   | jvm 1    | 2020/07/16 21:24:21 | W [c.i.x.d.a.ScheduledRequest    ] [04:24:21]: Uncaught Throwable invoking class com.inductiveautomation.xopc.drivers.allenbradley.requests.ABControlLogixReadRequest#receiveMessage: java.lang.NullPointerException 

It was obviously awhile before we noticed. When we did, looking at the threads we were able to determine one device connection was consuming 40-60% CPU. It is a CompactLogix PLC using the AB Legacy driver. Disabling and enabling this connection caused the CPU usage to drop back to normal levels. We didn’t take any thread dumps, but if we see this issue again we will.

Can anyone shed some light on the error we found in the logs or offer other ideas as to what caused this?

Ignition Version 8.0.10

Whatever happened is likely a bug in the legacy driver.

If you can get a thread dump and logs if/when it happens again that may help track down what’s going on.

We’ll definitely do that. Thanks for the input.