I mean this thing:
This is not the scrollbar (which is on the other side of the window). It seems to show the output of the last command run, but if I scroll back it seems to show "random" lines. The best explanation to its behavior is that it groups outputs that have been produced within a short time of each other but this only applies to the last command.
This appeared when I upgraded to Kubuntu 22.04 (so running Konsole 21.12.3 now).
Any hints?
It seems to be related to the option "Highlight lines coming into view" that you can set under "Scrolling" when you create a new profile:
It's not available to change in the default profile as that's not writable, so you only see that option when creating a new profile.