Anecdotally, I am no stranger to weird GTK error messages popping up occasionally in miniAudicle on whatever version of Linux I happen to be running.
Here is at least one example that I just got;
(miniAudicle:24570): Gtk-CRITICAL **: gtk_widget_event: assertion `WIDGET_REALIZED_FOR_EVENT (widget, event)' failed
(miniAudicle:24570): Gtk-CRITICAL **: gtk_widget_event: assertion `WIDGET_REALIZED_FOR_EVENT (widget, event)' failed