Why do I have this weird tile in middle of the hud?

Talking about the border. It goes away when changing screen, but doesn't look nice.

//edit: To top it off, it happens at random and sometimes is different tiles as well. But roughly in the same place.

Maybe it is a mis-placed HUB Element. Can you double check everything in your HUD Elements Tab an set any unused Elements to X: 0, Y:0, types: None?

Definitely not. I'm using all hud elements.