Xwayland crash
Usually reproduces when running a steam game (Age of Empire 2, using SteamPlay). From the game in fullscreen, alt-tab to another window, alt-tab again to the game.
(gdb) bt
#0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#1 0x00007fe02f786535 in __GI_abort () at abort.c:79
#2 0x000055cf7d61492a in OsAbort () at ../../../../os/utils.c:1350
#3 0x000055cf7d61a433 in AbortServer () at ../../../../os/log.c:879
#4 0x000055cf7d61b299 in FatalError (f=f@entry=0x55cf7d63f090 "Caught signal %d (%s). Server aborting\n") at ../../../../os/log.c:1017
#5 0x000055cf7d611d41 in OsSigHandler (signo=6, sip=<optimized out>, unused=<optimized out>) at ../../../../os/osinit.c:156
#6 <signal handler called>
#7 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#8 0x00007fe02f786535 in __GI_abort () at abort.c:79
#9 0x00007fe02f78640f in __assert_fail_base (fmt=0x7fe02f8e8ee0 "%s%s%s:%u: %s%sAssertion `%s' failed.\n%n", assertion=0x55cf7d626450 "xwl_window->present_window == window", file=0x55cf7d626420 "../../../../../hw/xwayland/xwayland-present.c", line=521, function=<optimized out>) at assert.c:92
#10 0x00007fe02f7940f2 in __GI___assert_fail (assertion=assertion@entry=0x55cf7d626450 "xwl_window->present_window == window", file=file@entry=0x55cf7d626420 "../../../../../hw/xwayland/xwayland-present.c", line=line@entry=521,
function=function@entry=0x55cf7d626480 <__PRETTY_FUNCTION__.25351> "xwl_present_flips_stop") at assert.c:101
#11 0x000055cf7d4bc793 in xwl_present_flips_stop (window=0x55cf8103ba40) at ../../../../../hw/xwayland/xwayland-present.c:521
#12 0x000055cf7d579d88 in present_wnmd_flips_stop (window=<optimized out>) at ../../../../present/present_wnmd.c:159
#13 0x000055cf7d57a6d0 in present_wnmd_flip_notify (crtc_msc=<optimized out>, ust=24206235332, vblank=0x55cf8168d3a0) at ../../../../present/present_wnmd.c:194
#14 present_wnmd_event_notify (window=<optimized out>, event_id=<optimized out>, ust=24206235332, msc=<optimized out>) at ../../../../present/present_wnmd.c:229
#15 0x000055cf7d4bc477 in xwl_present_sync_callback (data=0x55cf8168b590, callback=<optimized out>, time=<optimized out>) at ../../../../../hw/xwayland/xwayland-present.c:287
#16 0x00007fe02f6858ee in ffi_call_unix64 () from /usr/lib/x86_64-linux-gnu/libffi.so.6
#17 0x00007fe02f6852bf in ffi_call () from /usr/lib/x86_64-linux-gnu/libffi.so.6
#18 0x00007fe03089928d in ?? () from /usr/lib/x86_64-linux-gnu/libwayland-client.so.0
#19 0x00007fe030895ac9 in ?? () from /usr/lib/x86_64-linux-gnu/libwayland-client.so.0
#20 0x00007fe030896f94 in wl_display_dispatch_queue_pending () from /usr/lib/x86_64-linux-gnu/libwayland-client.so.0
#21 0x000055cf7d4b1d2b in xwl_read_events (xwl_screen=0x55cf7f2df8c0) at ../../../../../hw/xwayland/xwayland.c:814
#22 0x000055cf7d6126f1 in ospoll_wait (ospoll=0x55cf7f2d4f90, timeout=<optimized out>) at ../../../../os/ospoll.c:651
#23 0x000055cf7d60b773 in WaitForSomething (are_ready=0) at ../../../../os/WaitFor.c:208
#24 0x000055cf7d5dbbbc in Dispatch () at ../../../../include/list.h:220
#25 0x000055cf7d5dfdb6 in dix_main (argc=12, argv=0x7ffdd62a2448, envp=<optimized out>) at ../../../../dix/main.c:276
#26 0x00007fe02f78809b in __libc_start_main (main=0x55cf7d4b11b0 <main>, argc=12, argv=0x7ffdd62a2448, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffdd62a2438) at ../csu/libc-start.c:308
#27 0x000055cf7d4b11ea in _start ()
(gdb)