The version of x-d-p in unstable crashes when contacted by a Flatpak app ${APP_ID} which does not export a .desktop file named files/share/applications/${APP_ID}.desktop.
org.gnome.NautilusPreviewer on flathub (which I think is the same codebase
as gnome-sushi.deb) is a convenient reproducer for this.
The crash is fixed upstream in 1.20.2, but with only limited
functionality for apps like org.gnome.NautilusPreviewer that previously triggered this crash. I'm talking to upstream about a better fix.