Stops working unexpectedly

[Uqbar]

I am not able to reproduce this bug, but it seems to happen in conjunction with some KDE dialog.
The only thing I can do is to switch back to the text mode console (CTRL+ALT+F1) and run

    DISPLAY=:0.0 kwin_x11 --replace &

What I get as output from this program is then:

    Module 'org.kde.kwin.decoration' does not contain a module identifier directive - it cannot be protected from external registrations.
    QXcbConnection: XCB error: 8 (BadMatch), sequence: 1183, resource id: 10485765, major code: 42 (SetInputFocus), minor code: 0
    QXcbConnection: XCB error: 3 (BadWindow), sequence: 3292, resource id: 62914561, major code: 18 (ChangeProperty), minor code: 0
    QXcbConnection: XCB error: 3 (BadWindow), sequence: 3296, resource id: 62914562, major code: 18 (ChangeProperty), minor code: 0
   QXcbConnection: XCB error: 3 (BadWindow), sequence: 3300, resource id: 77594628, major code: 18 (ChangeProperty), minor code: 0
    ...

But I have no idea about the meaning.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: kwin-x11 4:5.5.5-0ubuntu1
Uname: Linux 4.14.15-041415-lowlatency x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
CurrentDesktop: KDE
Date: Thu Feb 1 10:43:49 2018
SourcePackage: kwin
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[shapirus (me-ngeefk4xayt3t4u)]

Same here on Ubuntu Bionic with kwin-x11=4:5.12.3-0ubuntu2.