@jobro: Not ignoring, just snowed under other things - sorry. In KDE you might want to change the compositor to something simpler, like xrender, or force full screen repaints. If you are willing to help us diagnose this more, it would be great if you could stop DisplayLink Service, and try other libevdi client to check if it also reproduces - e.g. monitorsim from
https://github.com/mlukaszek/evdipp
Thanks,
Michal