Mouse freezes when a second mouse is plugged in I use a wireless Logitech trackball for RSI reasons.  My wife uses a random dell usb mouse because she hates the trackball.  We have a single Mac mini and use fast user switching to change accounts.

On both accounts, the trackball stops tracking.  It'll move the cursor for a while and then stop mid-motion.  The buttons still work.  

On the login window, the mouse works.  When I log in from there, it works for up to a minute.  Then it dies again.  

I had no issues with this mouse on my previous machine (linux) and the issue started immediately when I switched to this mac.  

Equipment:  2014 Mac Mini running Sierra.  Logitech m570 trackball.  Generic dell usb other mouse.
I might have fixed this.  Not sure yet, but it's been usable for a whole 10 minutes which is a new record.

The fix?  I shuffled usbs until I found a permutation that works.  Didn't think that would be a problem in 2017, but here we are.