What is happening to my lawn?

photo

We get this line of dead grass in the same spot every year. The rest of the yard looks great. I’ve replaced the grass twice for various reasons and the sod I have now is about a year old. When replacing the grass new dirt went down so it’s not like there’s a huge rock right under the surface.

I put some black tape on the back of the fencepost in the picture just Incase the sun was bouncing there and burning—which sounds crazy.

Any ideas? Help me!