It appears related to https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3440

Funtoo 1.4 is referring to 3.36.7, that contains the issue.

$ head gnome-shell-3.36.7/src/calendar-server/gnome-shell-calendar-server.c -n 408

(...)

          g_variant_builder_add (&builder,
                                 "(ssbxxa{sv})",
                                 appt->id,
                                 appt->summary != NULL ? appt->summary : "",
                                 (gboolean) appt->is_all_day,
                                 (gint64) start_time,
                                 (gint64) end_time,
                                 extras_builder);     /// Ah-ha! Here's the double-free.

It appears the issue was never cherry-picked to later version of 3.36 and would require manual patching (see https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1855)

Not being a portage/ebuild expert, I would gladly appreciate if anyone could integrate the fix and show how it's done so I could contribute with similar backports.

epro.log

gnome-kit at commit dfbbba6496b7f8b9927bda4a4bc9e89cdf8c06d5