When I click on the lower zone mixer setup window arrow on top right hand side it just flashes and then gets greyed out?
I think you are going to have to provide more info and system specs if you want any meaningful help.
Yes, I think I know what you mean. It is just to the right of the Arrow Icon to make the lower zone mixer full size. I think that Steinberg realized that if you had those functions available the lower zone, the mixer wouldn’t scale properly. It it looks like they have disabled it on purpose. When you make the mixer full size it works, but that kind of defeats the purpose of having those functions. I’d like to have the control room available on the right side of the lower zone mixer, but I don’t think that is possible in the same way that you can do it in the full size mix window. While it may be a appear to be a bug, I think it is more like “unfinished” functionality or they just simply couldn’t make it work for the initial Cubase 9 release. That is just conjecture on my part though.
To be honest I run a three monitor system and the mixer has its own screen and I use the middle screen for editing and the arrange page on the left. The lower zone is quite pointless for me. However it is easily disabled and forgotten about.
One thing the lower zones capability to show send and inserts is a good one for me, in my workflow setting up inserts and sends is the middle stage of mixing and having the insert available in the project is handy, giving the mixconsole the room to show only send or other useful things while the insert and/or send are accessible through the low zone.