Showtime Nightly randomly segfaults on startup, even with no video (GtkMenuButton's "gtk_popover_set_position" causes a crash with "gtk_widget_get_parent")

Testing the latest nightly flatpak version on my desktop workstation with discrete open source AMD graphics (and another testbench with onboard AMD graphics), I realized one of the reasons Showtime won't launch from Nautilus about 20-30% of the time is because it segfaults on startup. It is a seemingly random occurrence, so it must be a race condition, possibly caused by GTK (see comment below).

While launching casually, the output looks like this:

$ flatpak run --devel --command=sh  org.gnome.Showtime.Devel 

[📦 org.gnome.Showtime.Devel tmp]$ gdb showtime
"/app/bin/showtime": not in executable format: file format not recognized

(gdb) run
Starting program:  No executable file specified.

(gdb) quit


[📦 org.gnome.Showtime.Devel tmp]$ showtime
root DEBUG - Starting org.gnome.Showtime.Devel v48.alpha (development)
root DEBUG - Python version: 3.12.8 (main, Nov 10 2011, 15:00:00) [GCC 14.2.0]
root DEBUG - GStreamer version: 1.24.10.0
root DEBUG - ─────────────────────────────────────

(python3:13): Gtk-CRITICAL **: 11:13:41.251: gtk_widget_get_parent: assertion 'GTK_IS_WIDGET (widget)' failed
(python3:13): Gtk-CRITICAL **: 11:13:41.251: gtk_widget_get_first_child: assertion 'GTK_IS_WIDGET (widget)' failed
(python3:13): GLib-GIRepository-CRITICAL **: 11:13:41.504: gi_repository_find_by_name: assertion 'GI_IS_REPOSITORY (repository)' failed

The app started started successfully, so I closed it and just tried again one second later:

[📦 org.gnome.Showtime.Devel tmp]$ showtime
root DEBUG - Starting org.gnome.Showtime.Devel v48.alpha (development)
root DEBUG - Python version: 3.12.8 (main, Nov 10 2011, 15:00:00) [GCC 14.2.0]
root DEBUG - GStreamer version: 1.24.10.0
root DEBUG - ─────────────────────────────────────
Segmentation fault (core dumped)

Demonstration video, showing how many tries it can sometimes take to crash it (I use the q shortcut key to easily/quickly close Showtime with the keyboard after successful startup):

2025-01-31_Showtime_random_segfault_on_startup