Thank you for this post!!
I have the same problem and it was driving me nuts. The problem was that I also bought a brand new mouse (Logitech MX Master) and actually returned the mouse and asked for a replacement.
Turns out it wasnt the mouse. Here come the strange part though. It happens far less often when I use the track pad.
It only happens in C9 though. No other app has the double click issue.
I really hope they fix this as it’s a real nightmare