Magic Mouse 2 vertical tracking issue on iMac 27 I have a weird issue that makes my Magic Mouse 2 usage experience very uncomfortable on iMac 27. 

The problem is: when I move the mouse vertically (up or down), tracking works very slow. That is: I have to raise and move my mouse 3-4 times to reach the bottom of the screen (assuming I started from the very top). 

On the other hand, moving in a horizontal direction with the same speed works like a charm. 

OS X Sierra, tracking speed is set to maximum and no third party applications used. 

Is there a way to fix this?
researching internet a minute ago with the exact same problem in the same hardware - iMac 27 late 2015 + Magic Mouse 2
I found the answer that solved my problem - just blew the optics's and vertical tracking speed is ok again. I should use an air compressed can but used my lungs instead but away from the mouse to avoid humidity as much as possible.it worked for me.