If you open the volume control on your local GNOME client, you see two instances of "ThinLinc Client". One is for playback and one is for recording, but you cannot tell the two apart. We should probably have both unique icons and text for the different streams.
Perhaps this is a bad design by GNOME. I've reported it to them here: https://gitlab.gnome.org/GNOME/gnome-control-center/issues/794 Let's see what they say.