I noticed the following issue due to USB resets causing my webcam to occaisionally connect and reconnect:

On UVC webcam connection (probably HID device), Xorg treats the webcam as a keyboard.

This misdetection seems to be related to X deciding it's not going to change focus based on mouse click (but the mouse pointer moves) and keyboard input having no effect.

If I unplug an replug my USB keyboard and mouse when then happens then X starts responding again.

I actually noticed this when I switched (live) to a webcam that doesn't reset, but as soon as I plugged in the webcam it was detected as a keyboard and X stopped responding to input, but once I unplugged and replugged my mouse keyboard things were fine again.