No operator error. I mark the chain link with a scribe to see where I broke it. Totally not there. When it broke on this ride, it was in two separate places.

I've been breaking chains with a tool for 30 years. I have it down pat. Hence my confusion. There was no skipping prior to it breaking. If your pinching the plates it will chug through the derailleur cage. It was smooth, the pins were spaced right.

Recap, it is not breaking where my tool has been. If it was, there would be no thread.