How can I determine where mouse input is coming from? Is there a way to log click events? No other mice are connected
This might be a case of defective trackpad. I had a very similar problem where the trackpad registered constant mouse click. You can quickly test that by connecting an external mouse, then go System Preferences > Accessibility > Mouse &amp; Trackpad > Checkmark "Ignore built-in trackpad...".

If the problem is with the built-in trackpad, the odd behaviour will stop at this point as long as external mouse is connected.