When using global Display scaling factor that is not an integer (1x or 2x), the konsole will commonly draw the current line a bit off (too high), leaving a thin line of white space underneath.
In the future, please attach a screenshot when reporting visual glitches. See https://community.kde.org/Get_Involved/Bug_Reporting#Screenshots_and_screen_recordings *** This bug has been marked as a duplicate of bug 373232 ***