Having multiple DEs installed (Gnome, Plasma, Cinnamon, MATE, XFCE4, Openbox and minor ones), some of them show strange behaviour probably related to not marked incompatibilities and/or dbus race conditions.
My main DE is XFCE, and this doesn't start xfce4-notifyd with session, having to start it manually. Plasma starts only partially, leaving a black screen with mouse cursor and nothing else, except when run within a nested Xephyr on XFCE. Gnome crashes after login, returning to gdm. In a nested Xephyr it starts partially without crashing, but without anything else. Cinnamon and MATE applications menu are completely empty, and MATE inner services (like setting wallpaper) don't work either.
Of course, I selected carefully which packages to install and noted no conflicts. Weirdest thing, I have another computer whose package set I cloned to this one and it doesn't show any problem. Since that computer has been running for some time already, it is retaining packages not available anymore on repo.