I have two vertically stacked monitors & under Wayland & now X, the right wallpaper will only show when apply system settings from right click menu. But, as soon as I close the wallpaper settings dialogue it reverts to out of order/sync. I have two folders, top & bottom & set to change every 10 minutes. Without respecting A-Z order they get outa sync.

Would this be a Plasma 5 bug?