After the last update to my Arch-derived Linux distro, Konsole no longer correctly renders the scrollbars. A quick search lead me to this change https://phabricator.kde.org/D11839 which I believe could be the culprit. The code change removes the subtraction of the scrollbar area from the painting of the window content background, meaning the area that should be scrollbar background would be painted black instead, which is exactly what I now see. The opaque test case in that review is not much a test case as the scrollbar background appears to be the same color as the window content. Try with a different theme and the fail should be quite obvious.
Can you provide your profile/colorscheme and perhaps a screenshot please?
Created attachment 112920 [details] example screenshot I am using the Kvantum theme with the Obsidian Coast color scheme. The attached screenshot shows a scrollbar in Konsole (left) adjacent to a scrollbar in Dolphin (right) for reference. The Scrollbar in Konsole has no background so it kinda falls into the content, the arrows almost disappear, and the trough in combination with the window border makes an unsightly double line. NB: The referenced review was the first candidate I found, but since then I have become aware of bug 393423, which looks more directly related from the description.
*** This bug has been marked as a duplicate of bug 393423 ***