Same here

Application: kwin_x11 (5.19.2)

Qt Version: 5.14.2
Frameworks Version: 5.71.0
Operating System: Linux 5.3.0-59-generic x86_64
Windowing system: X11
Distribution: KDE neon User Edition 5.19

-- Information about the crash:
<In detail, tell us what you were doing  when the application crashed.>

The crash can be reproduced sometimes.

-- Backtrace:
Application: KWin (kwin_x11), signal: Segmentation fault

[KCrash Handler]
#4  0x000055ab026cdc00 in  ()
#5  0x00007fe0b115afca in KWin::Workspace::workspaceEvent(xcb_generic_event_t*) (this=0x55ab0055e6e0, e=0x7fe0900749f0) at ./events.cpp:240
#6  0x00007fe0ae7ca4df in QAbstractEventDispatcher::filterNativeEvent(QByteArray const&, void*, long*) (this=<optimized out>, eventType=..., message=message@entry=0x7fe0900749f0, result=result@entry=0x7ffd33e0cc48) at kernel/qabstracteventdispatcher.cpp:488
#7  0x00007fe099ea7bac in QXcbConnection::handleXcbEvent(xcb_generic_event_t*) (this=this@entry=0x55ab00458fd0, event=event@entry=0x7fe0900749f0) at qxcbconnection.cpp:550
#8  0x00007fe099ea86d6 in QXcbConnection::processXcbEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x55ab00458fd0, flags=...) at qxcbconnection.cpp:1029
#9  0x00007fe099ecd32c in QXcbUnixEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x55ab004ab2a0, flags=...) at qxcbeventdispatcher.cpp:61
#10 0x00007fe0ae7cbd2a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (this=this@entry=0x7ffd33e0cda0, flags=..., flags@entry=...) at kernel/qeventloop.cpp:225
#11 0x00007fe0ae7d54a0 in QCoreApplication::exec() () at kernel/qcoreapplication.cpp:1383
#12 0x000055aafffcc3db in main(int, char**) (argc=<optimized out>, argv=0x7ffd33e0d018) at ./main_x11.cpp:479

Possible duplicates by query: bug 423319, bug 422899, bug 422558, bug 422275, bug 421762.

Report to https://bugs.kde.org/

I can also reproduce this reliably, although DrKonqi does not catch it. In order to reproduce, I simply activate the Present Windows hot corner after it has already been activated. after 1-3 attempts, this reliably produces a KWin segfault.

I run into the same problem. After a crash, I lose OpenGL rendering. When I go to settings -> compositor I can enable it by switching to XRender and then OpenGL again. As soon as I go to the hot corner, the same crash happens. Here some system information:
 
Operating System: Arch Linux
KDE Plasma Version: 5.19.2
KDE Frameworks Version: 5.71.0
Qt Version: 5.15.0
Kernel Version: 5.7.4-arch1-1
OS Type: 64-bit
Processors: 4 × Intel® Core™ i7-5600U CPU @ 2.60GHz
Memory: 11.4 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 5500

Created attachment 129742 [details]
New crash information added by DrKonqi

kwin_x11 (5.19.2) using Qt 5.15.0

- What I was doing when the application crashed:
I have set a hot corner shortcut to show windows on current desktop. The crash happens when using it for a second time (when it is supposed to hide the windows).

- Custom settings of the application:
Not sure if this is useful information, but I'm using the OpenGL 3.1 backend with the compositor. My GPU is an AMD Vega 56. I'm using Mesa version 20.1.1, Qt version 5.15 and KDE Frameworks 5.7.1.

-- Backtrace (Reduced):
#5  0x00007f67cf54cdcc in KWin::Workspace::workspaceEvent(xcb_generic_event_t*) (this=<optimized out>, e=0x7f67c001ab70) at /usr/include/qt5/QtCore/qvector.h:1041
#6  0x00007f67ce145057 in QAbstractEventDispatcher::filterNativeEvent(QByteArray const&, void*, long*) (this=<optimized out>, eventType=..., message=message@entry=0x7f67c001ab70, result=result@entry=0x7fffe67c2ad8) at kernel/qabstracteventdispatcher.cpp:488
#7  0x00007f67c841a571 in QXcbConnection::handleXcbEvent(xcb_generic_event_t*) (this=this@entry=0x55837e5d88b0, event=event@entry=0x7f67c001ab70) at qxcbnativeinterface.h:101
#8  0x00007f67c841ba86 in QXcbConnection::processXcbEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x55837e5d88b0, flags=...) at qxcbconnection.cpp:1003
#9  0x00007f67c843e2fc in QXcbUnixEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x55837e703070, flags=...) at qxcbeventdispatcher.cpp:61

Created attachment 129947 [details]
New crash information added by DrKonqi

kwin_x11 (5.19.2) using Qt 5.15.0

- What I was doing when the application crashed:
Entered Present Windows by hot corners. Crash happens when I exit the effect. Happens quite reliably every few times I do this.
- Custom settings of the application:
OpenGL 3.1 compositor (doesn't happen for XRender). Intel Graphics UHD 620, modesetting driver.

-- Backtrace (Reduced):
#5  0x00007efe2149bdcc in KWin::Workspace::workspaceEvent(xcb_generic_event_t*) (this=<optimized out>, e=0x7efe14007360) at /usr/include/qt5/QtCore/qvector.h:1041
#6  0x00007efe20094057 in QAbstractEventDispatcher::filterNativeEvent(QByteArray const&, void*, long*) (this=<optimized out>, eventType=..., message=message@entry=0x7efe14007360, result=result@entry=0x7ffec3be9758) at kernel/qabstracteventdispatcher.cpp:488
#7  0x00007efe1a37b571 in QXcbConnection::handleXcbEvent(xcb_generic_event_t*) (this=this@entry=0x560c05868b60, event=event@entry=0x7efe14007360) at qxcbnativeinterface.h:101
#8  0x00007efe1a37ca86 in QXcbConnection::processXcbEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x560c05868b60, flags=...) at qxcbconnection.cpp:1003
#9  0x00007efe1a39f2fc in QXcbUnixEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x560c0597bf00, flags=...) at qxcbeventdispatcher.cpp:61

I noticed one weird thing with this crash. It crashes almost every time if you exit the show windows screen by a hot corner. However it doesn't crash at all if you exit it by clicking on empty space.

Created attachment 129960 [details]
Clicking on the glow corner to trigger the crash.

(In reply to Roni Hokkanen from comment #6)
> I noticed one weird thing with this crash. It crashes almost every time if
> you exit the show windows screen by a hot corner. However it doesn't crash
> at all if you exit it by clicking on empty space.

In my case i need to click on the glowing corner to trigger it, just hovering the mouse over the corner again did nothing for me.

*** This bug has been marked as a duplicate of bug 423319 ***

Created attachment 130600 [details]
New crash information added by DrKonqi

kwin_x11 (5.19.4) using Qt 5.14.2

- What I was doing when the application crashed: Closing the android studio. Trying to use the hot corner to switch between applications

- Unusual behavior I noticed:
KDE NEON dark mode, NVIDIA driver, std kernel

-- Backtrace (Reduced):
#4  std::__find_if<int const*, __gnu_cxx::__ops::_Iter_equals_val<int const> > (__pred=..., __last=0x357f80a401ee84, __first=0x357f80a401e580) at /usr/include/c++/7/bits/stl_algo.h:120
#5  std::__find_if<int const*, __gnu_cxx::__ops::_Iter_equals_val<int const> > (__pred=..., __last=<optimized out>, __first=<optimized out>) at /usr/include/c++/7/bits/stl_algo.h:162
#6  std::find<int const*, int> (__val=@0x7ffcc6fbf1e8: 6, __last=<optimized out>, __first=<optimized out>) at /usr/include/c++/7/bits/stl_algo.h:3908
#7  QVector<int>::contains (this=this@entry=0x7ffcc6fbf1f0, t=@0x7ffcc6fbf1e8: 6) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qvector.h:1045
#8  0x00007f4bc27fc2b7 in KWin::Workspace::workspaceEvent (this=0x55794cef2470, e=0x7f4ba402add0) at ./events.cpp:240