Mutter trigger critical errors on Keyboard changes under X11
Any keyboard state change triggers this error in current mutter.
(gnome-shell:16054): Clutter-CRITICAL **: 17:51:30.380: _clutter_stage_queue_event: assertion 'CLUTTER_IS_STAGE (stage)' failed
Just run it in X11 and run it or change the keyboard state (locks), and you'd get this error.