I had some troubles after install Gnome 3.20, like GTK3 apps desabled scrollbars, and theming. I cant use the Zuki, Arc or Vertex theme, even the 3.20 versions of it. Sorry for my bad english, and cheers from Brazil!
First, don't ever install different desktop environments on a computer you use daily. I have always found the claims about compatibility to be false crapware advertisement. ( not saying Ubuntu is cr*p at all )
That points to Purge all desktop environments except one and reinstalling The Chosen One to run the automatic configuration. Haven't done that myself. So you'll need to get familiar with CTRL + ALT + F1 first, in case you need to try the default desktop environment and additionally, uninstalling the default in the first place will uninstall many things so try keeping the default one, I think that's what the distribution author wants.
Easier than that use Ubuntu GNOME instead. No need to remind that Linux distributions can be tested before installation and should be. Don't expect the experience of Mac nor Windows in Linux or BSD operative systems. Here in the other side you get better results from understanding what you're doing, if you don't have the time to dive in all techie stuff then get a friend or hire someone. You could also buy a computer preinstalled with your OS of choice but I think it's not allowed to refer products here.
I don't plan to buy Linux pre-installed for the lack of UEFI but that's me.
Well I know apps got no money XD