Why are some of my screen-recording/capturing/sharing applications (or app features) not working in Ubuntu 17.10 (and later releases)?

Ubuntu 17.10 by default lets users log in to a GNOME environment on a Wayland session. You may check whether you're logged into a Wayland session instead of an Xorg (X11) session by running the following command in Terminal:

echo $XDG_SESSION_TYPE

Applications which are not compatible with Wayland yet run under a XWayland compatibility layer. But advanced applications, which depend on and/or control X11 server "too much" (screen-capturing/recording etc.), might fail to run in a Wayland session.

As a workaround you may switch back to an Xorg session.