Meeting - Half screen on secondary monitor

Hi guys, I've a problem.

I've 2 monitor, the main with 1920x1080 and the secondary with 4k resolution (3840x2160).

The problem is that the secondary 4k monitor is only shared for the top half.
And when I share the entire screen or by selecting the individual windows, is only shared what lies in the upper half, all that is in the bottom half is black. 

The problem only resolved if imposed 4k as the main screen, but for what I do I can not.

Solutions?

Sorry for my bad english