I’ve run into several bugs with Unity UI since the latest update. Scrollbars flipping upside down (they go to normal once you run the game), Moving objects within panels can throw errors if you move outside of the bounds of the panel accidentally (which also makes the image on the panel invisible without any way of fixing it, except to create a new panel), and now yellow arrows showing up out of nowhere… https://s30.postimg.org/w1ve1u7a9/Capture.jpg
I noticed this happens on Canvas Scaler when using Constant Physical Size. Seems like it doesn’t update the canvas scale until you run it at least one, and it resets after compile. This is a bug. To circumvent, just press play.
What is the error? Typically, this is the intended result of errors - stop what is happening because something is clearly broken/wrong.
These are Navigation visualizers, you can toggle it off.
https://docs.unity3d.com/Manual/script-SelectableNavigation.html