Unable to resize 2 snapped windows simultaneously

I got a DELL XPS 15 a week ago. It doesn't let me resize 2 snapped windows simultaneously.

Specifically, this doesn't happen :-

I'm having to manually resize the other window every time i resize one. 

I have already tried to turn off and on the settings in multitasking :-

I use this feature regularly and need a solution ASAP.

Thanks