Unknown line location

[need answer]

As you can see from the screen shot, there is a upside down U-shaped line. Also, all my layers are not visible and locked.

I cannot find the reason for this line. Any suggestions? First time this has ever happened in my work.

[Jacob Bugge]

need answer,

The screenshot is tiny, can you enlarge so helpers can see what is in it apart from the U shape?

Just to make sure: is it still there if you scroll up/down to get it out of view and then scrool back?

And maybe even sillier: is it still there is you hold Ctrl/Cmd and press E to toggle between GPU and CPU, you can toggle back?