Activity Monitor is unuseable because it's freezing mouse cursor when launched A weird problem started happening on my system in recent days (can't remember exactly). When I launch Activity Monitor, mouse pointer freezes and can't move normally until I kill Activity Monitor by using keyboard.
It works OK otherwise.
OS X version is 10.11.6 (15G1108). I have also installed SmoothMouse.
EDIT:
I removed SmoothMouse by issuing command brew cask zap smoothmouse, now the mouse cursor can move while Activity Monitor is opened, but Activity Monitor itself is still freezing and is barely usable.
This problem went away after I rebooted the system. (It was running for several weeks without rebooting before).

This clearly indicates that OS X just can't handle long uptime, because Apple cares more about bells and whistles than stability. :(