Error notifications are shown for "kdialog". With the following message "The Window Switcher installation is broken, resources are missing. Contact your distribution about this." The error notification appeared around 5-10 times. I wasn't able to pinpoint exact steps to reproduce this error. SOFTWARE/OS VERSIONS Operating System: KDE neon 5.19 KDE Plasma Version: 5.19.5 KDE Frameworks Version: 5.73.0 Qt Version: 5.15.0 Kernel Version: 5.3.0-51-generic OS Type: 64-bit Processors: 8 × Intel® Core™ i5-8250U CPU @ 1.60GHz Memory: 7.7 GiB of RAM Graphics Processor: Mesa Intel® UHD Graphics 620
It seems that the error appears on some of the Alt-Tabs, which is bound to "Walt Through Windows" in System Settings > Shortcuts > System Services > Kwin.
kdialog is only the external tool to allow kwin to display non-blocking dialogs.
Haven't encountered this error since, so closing the ticket.