And now that button suddenly showed up there in the lower zone, and I have no idea why it happen? 
Hi,
On the left side on the top, there is the the dots button. Use it to show/hide toolbar of the Lower Zone MixConsole.
I’ve almost the same issue not by splitting regions but with nudging or resizing crossfades. To be precise, I’m on Nuendo, but I don’t find anything similar in the Nuendo forum. Some people is saying the reason of my issue is that I’m on a mac.
Here’s the video link the shows a similar issue to yours. I’m still struggling to find a solution. For Nudging crossfaeds I use macros like this one:
Nude corssfate left. Starting point is to select the region on the right side of crossfade.
Nudge - Start left
Navigate - Left
Nudge - End left
Navigate - Right
