@9c59d669 @a6ff0b2b Wild theory based on a bit of experience working with USB HID input: Newer mice have something like a “high precision“ mode and a “low precision” mode for big and small movements and when the screen resolution is high enough, macOS gets confused between the two trying to map your big and small movements to screen pixels. Something like this is the only way I can explain the dramatic window jitter despite what appears to be a fairly smooth drag movement in the video… 

 @b29bfecf Don't forget about the requirement that multiple users be logged in at the same time! 

 @a6ff0b2b That’s just a macOS bug. :) If you want more wild speculation, they run a different version of the window manager when multiple users are logged in. Kind of like how Windows used to have a uni-processor and a multi-processor kernel and you’d boot into whatever the hardware needed.