Running

    lsb_release -rd
        Description:    openSUSE Leap 15.0
        Release:        15.0

journactl fills with these

    Nov 09 21:21:28 pg.loc plasmashell[2876]: qt.qpa.xcb: QXcbConnection: XCB
error: 2 (BadValue), sequence: 6410, resource id: 62914566, major code: 142
(Unknown), minor code: 3

lots

    journalctl | grep "qt.qpa.xcb: QXcbConnection: XCB error: 2 (BadValue),
sequence:" | wc -l
        47122

These/similar spamming log message have been reported for years, with everybody
pointing at someone else

    https://bugs.kde.org/show_bug.cgi?id=366421
    https://forum.qt.io/topic/55144/qxcbconnection-xcb-error-qwarning
    https://bugreports.qt.io/browse/QTBUG-55167
    https://bugzilla.redhat.com/show_bug.cgi?id=1497564
https://bugs.archlinux.org/task/57497

Finally, the last link suggests patches were made available for Fedora

    https://bugzilla.redhat.com/show_bug.cgi?id=1497564#c11

, i.e., at the distro.

Here, on Opensuse, with

    rpm -q --whatprovides /usr/bin/plasmashell
      plasma5-workspace-5.14.3-lp150.429.1.x86_64

(from,
http://download.opensuse.org/repositories/KDE:/Frameworks5/openSUSE_Leap_15.0)

this
    cat /etc/xdg/QtProject/qtlogging.ini
        [Rules]
        qt.qpa.xcb.xcberror=false

has no effect on these messages.