Happens to me sometimes when I tab out during load. Have been backing up my LuaUI folder for years due to this.
The problem is that the widgets are automatically repositioned if they are off-screen, so if you play on a smaller screen for once, it will push all your widgets together. This will be stored as new layout even if you go back to the bigger screen. So I have multiple LuaUI folders for the different screen resolutions that I'm switching between (because Laptop). The proper solution would be to have a custom UI preset that would reposition the widgets relative to the screen resolution.
I think the missplaced widgets might occur because the game reports a 0x0 screen resolution temporarily after loading, leading to all widgets being shoved into the 0x0 top left corner.