In general using multiple desktop environments can cause issues, I don't know how it is in the ubuntu world, but usually there's 2 packages akin to something like the following:
desktopenvironmentdesktopenvironment_settingsSo say, cinnamon and cinnamon_settings, now this is fine when you just have cinnamon, but if you then install gnome, it'll want gnome_settings.
But the trouble is that cinnamon_settings and gnome_settings 'clash' in a few subtle ways, because they both configure some of the same underlying things, so the state becomes a bit of a mess, and it's usually a bad idea to operate two different DE's. There is one work-around though, if you have two users, sayuser_gnome, and user_cinnamon then they each have their own underlying configurations and you can avoid the clash.
This is of course not a very practical thing to do, and you should commit to one DE or another. Or make another user account user_playground to mess around experimenting with other DE's.