And a fresh retrace today:

Core was generated by `/home/dan/git/gnome-shell/build/tmp-introspectcxwjenqm/Shell-0.1 --introspect-d'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f0586db711f in type_check_is_value_type_U (
    type=type@entry=1694390208) at ../../../../gobject/gtype.c:4156
4156	../../../../gobject/gtype.c: No such file or directory.
[Current thread is 1 (Thread 0x7f057dcc21c0 (LWP 18932))]
(gdb) bt
#0  0x00007f0586db711f in type_check_is_value_type_U
    (type=type@entry=<error reading variable: Cannot access memory at address 0x64fe57e8>) at ../../../../gobject/gtype.c:4156
#1  0x00007f0586db711f in g_type_check_is_value_type
    (type=type@entry=<error reading variable: Cannot access memory at address 0x64fe57e8>) at ../../../../gobject/gtype.c:4192
#2  0x00007f0586da8b10 in g_signal_newv
    (signal_name=signal_name@entry=0x7f0586fd9bae "startup-sequence-changed", itype=itype@entry=0x559364fe55d0 [ShellWindowTracker], signal_flags=G_SIGNAL_RUN_LAST, class_closure=0x0, accumulator=0x0, accu_data=0x0, c_marshaller=0x0, return_type=0x4 [void], n_params=1, param_types=0x559364fdf3e0)
    at ../../../../gobject/gsignal.c:1672
#3  0x00007f0586da9964 in g_signal_new_valist
    (signal_name=signal_name@entry=0x7f0586fd9bae "startup-sequence-changed", itype=itype@entry=0x559364fe55d0 [ShellWindowTracker], signal_flags=<optimised out>, class_closure=<optimised out>, accumulator=<optimised out>, accu_data=<optimised out>, c_marshaller=0x0, return_type=0x4 [void], n_params=1, args=0x7ffc1ddd2880) at ../../../../gobject/gsignal.c:1902
#4  0x00007f0586da9a4e in g_signal_new
    (signal_name=0x7f0586fd9bae "startup-sequence-changed", itype=0x559364fe55d0 [ShellWindowTracker], signal_flags=<optimised out>, class_offset=<optimised out>, accumulator=<optimised out>, accu_data=<optimised out>, c_marshaller=0x0, return_type=0x4 [void], n_params=1) at ../../../../gobject/gsignal.c:1437
#5  0x00007f0586fcb20e in shell_window_tracker_class_init
    (klass=0x559364fe5730) at ../src/shell-window-tracker.c:112
#6  0x00007f0586fcafca in shell_window_tracker_class_intern_init
    (klass=0x559364fe5730) at ../src/shell-window-tracker.c:51
#7  0x00007f0586db374b in type_class_init_Wm
    (pclass=0x50 [g_type: GObject], node=0x559364fe55d0)
    at ../../../../gobject/gtype.c:2232
#8  0x00007f0586db374b in g_type_class_ref (type=<optimised out>)
    at ../../../../gobject/gtype.c:2947
#9  0x0000559364ad20e5 in dump_properties
    (type=0x559364fe55d0 [ShellWindowTracker], out=0x559364fcc510 [GLocalFileOutputStream])
    at /home/dan/git/gnome-shell/build/tmp-introspectcxwjenqm/Shell-0.1.c:137
#10 0x0000559364ad1b83 in dump_object_type
    (out=0x559364fcc510 [GLocalFileOutputStream], symbol=<optimised out>, type=0x559364fe55d0 [ShellWindowTracker])
    at /home/dan/git/gnome-shell/build/tmp-introspectcxwjenqm/Shell-0.1.c:260
#11 0x0000559364ad1b83 in dump_type
    (out=0x559364fcc510 [GLocalFileOutputStream], symbol=<optimised out>, type=0x559364fe55d0 [ShellWindowTracker])
    at /home/dan/git/gnome-shell/build/tmp-introspectcxwjenqm/Shell-0.1.c:402
#12 0x0000559364ad1b83 in dump_irepository
    (error=0x7ffc1ddd2ae0, arg=<optimised out>)
    at /home/dan/git/gnome-shell/build/tmp-introspectcxwjenqm/Shell-0.1.c:547
#13 0x0000559364ad1b83 in main (argc=<optimised out>, argv=<optimised out>)
    at /home/dan/git/gnome-shell/build/tmp-introspectcxwjenqm/Shell-0.1.c:610
(gdb)