It will happen to every PLC programmer sooner or later: a seemingly inexplicable sequence of events in the code that happens too fast to see. It is a bit like watching a skilled sleight-of-hand magician. You know something is happening, but you have no idea what that something is exactly.
This is a companion discussion topic for the original entry at https://www.solisplc.com/tutorials/plc-troubleshooting-using-trends-in-allen-bradley-rslogix-studio-5000