I am not sure where to report bugs. We have encountered a few issues with Cocos Creator when used on a 4K display and both are close to show stoppers:
We are unable to change node parenting in the Node Tree as the editor does not correctly detect the location of the final drop event.
Items dropped onto the Scene layout likewise are placed in some offscreen location rather than where the mouse was released.
When launched in the default browser, the Canvas renderer creates way too large such that most of the game is unavailable off screen. This might be a chrome bug.
A lot of apps have problems when using multiple monitors of different dpi. Microsoft suggests using only one type of dpi. I know because I had my 4k connected to my windows machine until i gave up and moved it to my mac instead.
I had the same setup, center 4k and two low dpi monitors on the sides. I had nothing but problems with that setup.
Try temporarily removing the two lower dpi monitors and see if it works.
