How to interpret PM861 Controller log
I assume that you mean "Hot swapped" is shown in the log as "Hot removal of CEX module at position 1 detected". I don't see that anywhere else in the log and if this issue has happened twice since November, I would expect to see the same message prior to the CPU stopping. I would lean more towards an issue in the CPU. According to document 3BSE040269, this CPU model number PM861K01 is near the end of the limited phase which is short of being in the obsolete phase. I know that v5.0 entered into the limited phase as well. You may want to consider an upgrade to hardware and software in the Active lifecycle phase.
Just as an FYI.. We had a CPU that failed and would not allow us to even connect to it. We had no choice but to replace it. If you do decide to replace the CPU, make sure to write down values such as internal PID setpoints or any value that may have changed from its intial value. When we pressed the Init button, the CPU reverted back to the initial value. The internal PID setpoints reverted back to 0 and we had some issues starting up the line again. Best of luck!