I thought I had a reasonable understancing of GFCI devices.
My first problems were when I was using GFCI for protection in a hydroponic greenhouse. There was a lot of plant nutrient which was essentially salt water. I had immersible pumps in the solution that were on a timer. They tended to trip when the timer turned the pumps off. These used pumps with a separate ground wire.
I rationalized that the inductive kick somehow led to leakage to ground. By placing a capacitor between hot and neutral, was able to get rid of the unwanted trips.
More recently, I was using a Water Pik in the bathroom. It used a two wire connection with no separate grounding conductor. GFCI should still work well. There never was tripping when I turned the device off. When I remove the plug from the wall socket with device switched off was when I would get occasional trips. I rationalized that in the bathroom environment there may have been just enough surface moisture to connect to my hand.
Today was different. I turned off the Water Pik. My hands were relatively dry. I grabbed the plug as far away from the socket as I could while getting a firm grip on the plug structure so as not to put a strain on the wires. When I disconnected the plug, I got a trip AFTER the plug was disconnected. I guess that the time delay between the time I saw the plug's prongs and the click was about 1/5 of a second.
Does anyone here have reasonable scenarios for what happened?