Theme is not using the stretch element indicator in panel-background.svg
Created by: Jonchun
This causes a weird tiling effect to occur with panel backgrounds:
Source: https://bugs.kde.org/show_bug.cgi?id=419619
is not Latte or Plasma fault. You are using McMojave plasma theme, its panel-background.svg does not contain the stretch element indicator, check out other plasma themes to see how this is achieved.