Our backup tool attempts to unlock the volume of the inserted USB drive itself, and displays a polkit prompt stating `Enter a passphrase to unlock the volume` to unlock it, but since we enabled auto-mounting of removable media (#15900, #15767) that prompt will race against GNOME's own unlock prompt stating `Authentication Required`. Never having tested this tool or looked at its code I'm not entirely sure, but perhaps a fix would be to stop trying to unlock the device itself and instead wait for GNOME to do it? Actually, it could check if `org.gnome.desktop.media-handling.automount` is set to determine what to do. This mess was detected by the automated test suite, yay!