We can't do anything with crash reports without backtraces, sorry.

You should see a sad face icon in the system tray after it crashes which can be used to report the bug.

(In reply to David Edmundson from comment #1)
> We can't do anything with crash reports without backtraces, sorry.
> 
> You should see a sad face icon in the system tray after it crashes which can
> be used to report the bug.

I didn't actually get a crash notification as I normally would for other programs.  What I can give is the output from console crashing while running kwin.  Not sure how to give much more.

$ kwin
QXcbConnection: XCB error: 3 (BadWindow), sequence: 178, resource id: 39845894, major code: 20 (GetProperty), minor code: 0
QXcbConnection: XCB error: 3 (BadWindow), sequence: 191, resource id: 39845894, major code: 20 (GetProperty), minor code: 0
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setWindow: Painter not active
QPainter::setClipRect: Painter not active
QPainter::save: Painter not active
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setPen: Painter not active
QPainter::setBrush: Painter not active
QPainter::setClipRect: Painter not active
QPainter::drawRects: Painter not active
QPainter::restore: Unbalanced save/restore
QPainter::begin: Paint device returned engine == 0, type: 3
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setWindow: Painter not active
QPainter::setClipRect: Painter not active
QPainter::save: Painter not active
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setPen: Painter not active
QPainter::setBrush: Painter not active
QPainter::setClipRect: Painter not active
QPainter::drawRects: Painter not active
QPainter::restore: Unbalanced save/restore
kwin_core: Compositing is not possible
The X11 connection broke: No error (code 0)
XIO:  fatal IO error 39 (Directory not empty) on X server ":0"
      after 3293 requests (3293 known processed) with 0 events remaining.
QObject::~QObject: Timers cannot be stopped from another thread
QtDBus: cannot relay signals from parent QObject(0x555ae49fdcc0 "") unless they are emitted in the object's thread QThread(0x555ae4977db0 ""). Current thread is QSGRenderThread(0x7f4ff80154f0 "").

(In reply to Thomas from comment #2)
> I didn't actually get a crash notification as I normally would for other
> programs...

Do this: https://community.kde.org/KWin/Debugging#Debug_.26_log_KWin_.28or_any_process.29_via_gdb

$ gdb --pid `pidof kwin_x11` 2>&1
GNU gdb (Ubuntu 8.1-0ubuntu3) 8.1.0.20180409-git
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".
Attaching to process 2753
[New LWP 2754]
[New LWP 2755]
[New LWP 2756]
[New LWP 2758]
[New LWP 2762]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007f4c6fb65cf6 in __GI_ppoll (fds=0x5610d59c8c38, nfds=4, timeout=<optimized out>, sigmask=0x0)
    at ../sysdeps/unix/sysv/linux/ppoll.c:39
39      ../sysdeps/unix/sysv/linux/ppoll.c: No such file or directory.
(gdb) continue
Continuing.
[Thread 0x7f4c4ef89700 (LWP 2756) exited]
[New Thread 0x7f4c4ef89700 (LWP 2858)]
[Thread 0x7f4c4ffff700 (LWP 2755) exited]
[Thread 0x7f4c4ef89700 (LWP 2858) exited]
[Thread 0x7f4c4d7a5700 (LWP 2758) exited]
[Thread 0x7f4c56880700 (LWP 2754) exited]
[Thread 0x7f4c70209cc0 (LWP 2753) exited]
[Inferior 1 (process 2753) exited with code 01]
(gdb) bt
No stack.
(gdb) quit

I've realized that none of my desktop effects were working.  I went in to the compositor settings and it showed that OpenGL detection was disabled due to a previous Kwin crash.  I enabled that again, rebooted, and everything is fine.