Shotcut installed from flathub has this problem. On snap version there is no problem, but its old version…
So everything works only in AppImage version, but i don’t like it… i prefer flatpak (or repo).
Mint 18.3 Cinnamon
Flatpak, Snaps and AppImages are still rather new and still somewhat buggy from what I have experienced. Run flatpak --version from a terminal and see if you have the latest version. I now have 0.11.7 and it works better.
-=Ken=-