Power manager does not grab any keys when started via xdg autostart

...on my Acer Chromebook 14 CB3-431 (Edgar). This issue is described in detail (with logs provided) in this xfce forum thread. Here's also the backtrace taken roughly 10 seconds after xfce is started (I barely know any C nor how to use gdb, so please let me know if there is more debug info I need):

(gdb) attach 1901
Attaching to process 1901
[New LWP 1909]
[New LWP 1910]
Error while reading shared library symbols for /usr/lib/libpthread.so.0:
Cannot find user-level thread for LWP 1910: generic error
0x00007f69e7a4637f in poll () from /usr/lib/libc.so.6
(gdb) thread apply all -c bt full

Thread 3 (LWP 1910 "gdbus"):
#0  0x00007f69e7a4637f in poll () at /usr/lib/libc.so.6
#1  0x00007f69e7e91ae8 in  () at /usr/lib/libglib-2.0.so.0
#2  0x00007f69e7e3d593 in g_main_loop_run () at /usr/lib/libglib-2.0.so.0
#3  0x00007f69e80a9558 in  () at /usr/lib/libgio-2.0.so.0
#4  0x00007f69e7e6c0c1 in  () at /usr/lib/libglib-2.0.so.0
#5  0x00007f69e7b2a299 in start_thread () at /usr/lib/libpthread.so.0
#6  0x00007f69e7a51053 in clone () at /usr/lib/libc.so.6

Thread 2 (LWP 1909 "gmain"):
#0  0x00007f69e7a4637f in poll () at /usr/lib/libc.so.6
#1  0x00007f69e7e91ae8 in  () at /usr/lib/libglib-2.0.so.0
#2  0x00007f69e7e3b781 in g_main_context_iteration () at /usr/lib/libglib-2.0.so.0
#3  0x00007f69e7e3b7d2 in  () at /usr/lib/libglib-2.0.so.0
#4  0x00007f69e7e6c0c1 in  () at /usr/lib/libglib-2.0.so.0
#5  0x00007f69e7b2a299 in start_thread () at /usr/lib/libpthread.so.0
#6  0x00007f69e7a51053 in clone () at /usr/lib/libc.so.6

Thread 1 (LWP 1901 "xfce4-power-man"):
#0  0x00007f69e7a4637f in poll () at /usr/lib/libc.so.6
#1  0x00007f69e7e91ae8 in  () at /usr/lib/libglib-2.0.so.0
#2  0x00007f69e7e3d593 in g_main_loop_run () at /usr/lib/libglib-2.0.so.0
#3  0x00007f69e85f561f in gtk_main () at /usr/lib/libgtk-3.so.0
#4  0x00005622424fad87 in xfpm_start (bus=0x56224469e170, client_id=0x0, dump=0) at xfpm-main.c:248
        manager = 0x56224487a100
        error = 0x0
        __func__ = "xfpm_start"
#5  0x00005622424fb774 in main (argc=1, argv=0x7ffca9ff6098) at xfpm-main.c:458
        bus = 0x56224469e170
        error = 0x0
        proxy = 0x0
        octx = 0x5622444b8090
        run = 0
        quit = 0
        config = 0
        version = 0
        reload = 0
        daemonize = 0
        debug = 1
        dump = 0
        client_id = 0x0
        option_entries = {{long_name = 0x56224251a39b "run", short_name = 114 'r', flags = 1, arg = G_OPTION_ARG_NONE, arg_data = 0x7ffca9ff5d58, description = 0x0, arg_description = 0x0}, {long_name = 0x56224251a39f "daemon", short_name = 0 '\000', flags = 2, arg = G_OPTION_ARG_NONE, arg_data = 0x7ffca9ff5d6c, description = 0x56224251a3a6 "Daemonize", arg_description = 0x0}, {long_name = 0x56224251a3b0 "debug", short_name = 0 '\000', flags = 2, arg = G_OPTION_ARG_NONE, arg_data = 0x7ffca9ff5d70, description = 0x56224251a3b6 "Enable debugging", arg_description = 0x0}, {long_name = 0x56224251a3c7 "dump", short_name = 0 '\000', flags = 2, arg = G_OPTION_ARG_NONE, arg_data = 0x7ffca9ff5d74, description = 0x56224251a3cc "Dump all information", arg_description = 0x0}, {long_name = 0x56224251a3e1 "restart", short_name = 0 '\000', flags = 2, arg = G_OPTION_ARG_NONE, arg_data = 0x7ffca9ff5d68, description = 0x56224251a3f0 "Restart the running instance of Xfce power manager", arg_description = 0x0}, {long_name = 0x56224251a423 "customize", short_name = 99 'c', flags = 2, arg = G_OPTION_ARG_NONE, arg_data = 0x7ffca9ff5d60, description = 0x56224251a42d "Show the configuration dialog", arg_description = 0x0}, {long_name = 0x56224251a44b "quit", short_name = 113 'q', flags = 2, arg = G_OPTION_ARG_NONE, arg_data = 0x7ffca9ff5d5c, description = 0x56224251a450 "Quit any running xfce power manager", arg_description = 0x0}, {long_name = 0x56224251a474 "version", short_name = 86 'V', flags = 2, arg = G_OPTION_ARG_NONE, arg_data = 0x7ffca9ff5d64, description = 0x56224251a47c "Version information", arg_description = 0x0}, {long_name = 0x56224251a490 "sm-client-id", short_name = 0 '\000', flags =1, arg = G_OPTION_ARG_STRING, arg_data = 0x7ffca9ff5d80, description = 0x0, arg_description = 0x0}, {long_name = 0x0, short_name = 0 '\000', flags = 0, arg = G_OPTION_ARG_NONE, arg_data = 0x0, description = 0x0, arg_description = 0x0}}