Did not know what triggered the crash but I only see Xwayland assertion and its crash. Since the original report on https://bugs.freedesktop.org/show_bug.cgi?id=106930 is stagnant and does not mention a kwin bug report I thought it is useful to have a reference here.

Relevant part from the logs

> kwin_wayland: /build/kwin/src/kwin-5.14.1/scene.cpp:412: void KWin::Scene::windowClosed(KWin::Toplevel*, KWin::Deleted*): Assertion `m_windows.contains(c)' failed.
> QSocketNotifier: Invalid socket 13 and type 'Read', disabling...
> QSocketNotifier: Invalid socket 19 and type 'Read', disabling...
> Xwayland: ../xorg-server-1.20.2/hw/xwayland/xwayland-present.c:521: xwl_present_flips_stop: Assertion `xwl_window->present_window == window' failed.
> (EE) 
> (EE) Backtrace:
> (EE) 0: /usr/bin/Xwayland (0x55ad4b942000+0x6ed1d) [0x55ad4b9b0d1d]
> (EE) 1: /usr/bin/Xwayland (0x55ad4b942000+0x6f730) [0x55ad4b9b1730]
> (EE) 2: /usr/lib/libc.so.6 (0x7f15700f7000+0x37e00) [0x7f157012ee00]
> (EE) 3: /usr/lib/libc.so.6 (gsignal+0x10f) [0x7f157012ed7f]
> (EE) 4: /usr/lib/libc.so.6 (abort+0x125) [0x7f1570119672]
> (EE) 5: /usr/lib/libc.so.6 (0x7f15700f7000+0x22548) [0x7f1570119548]
> (EE) 6: /usr/lib/libc.so.6 (0x7f15700f7000+0x30396) [0x7f1570127396]
> (EE) 7: /usr/bin/Xwayland (0x55ad4b942000+0x1854cb) [0x55ad4bac74cb]
> (EE) 8: /usr/bin/Xwayland (0x55ad4b942000+0xd433e) [0x55ad4ba1633e]
> (EE) 9: /usr/bin/Xwayland (0x55ad4b942000+0xd45b5) [0x55ad4ba165b5]
> (EE) 10: /usr/bin/Xwayland (0x55ad4b942000+0xd769f) [0x55ad4ba1969f]
> (EE) 11: /usr/bin/Xwayland (0x55ad4b942000+0x100108) [0x55ad4ba42108]
> (EE) 12: /usr/bin/Xwayland (0x55ad4b942000+0x145805) [0x55ad4ba87805]
> (EE) 13: /usr/bin/Xwayland (0x55ad4b942000+0x145e5b) [0x55ad4ba87e5b]
> (EE) 14: /usr/bin/Xwayland (0x55ad4b942000+0x104c0a) [0x55ad4ba46c0a]
> (EE) 15: /usr/bin/Xwayland (0x55ad4b942000+0x10918c) [0x55ad4ba4b18c]
> (EE) 16: /usr/bin/Xwayland (0x55ad4b942000+0x10cd49) [0x55ad4ba4ed49]
> (EE) 17: /usr/bin/Xwayland (0x55ad4b942000+0x1308cd) [0x55ad4ba728cd]
> (EE) 18: /usr/bin/Xwayland (0x55ad4b942000+0x6dcb1) [0x55ad4b9afcb1]
> (EE) 19: /usr/bin/Xwayland (0x55ad4b942000+0x135c90) [0x55ad4ba77c90]
> (EE) 20: /usr/bin/Xwayland (0x55ad4b942000+0x3010d) [0x55ad4b97210d]
> (EE) 21: /usr/lib/libc.so.6 (__libc_start_main+0xf3) [0x7f157011b223]
> (EE) 22: /usr/bin/Xwayland (0x55ad4b942000+0x3113e) [0x55ad4b97313e]
> (EE) 
> (EE) 
> Fatal server error:
> (EE) Caught signal 6 (Aborted). Server aborting
> (EE)