Have you checked for grubs or perhaps a large buried object such as a rock? You can check for grubs by cutting out a 1 sq ft piece of turf and lifting it up to look for them about 1-3 inches.

If you don't find anything.... while you have bat piece of turf lifted up, you could try to stick a long screwdriver as deep as you can to see if you strike something like a rock, brick, stump, tree or shrub roots etc. You never know!

Do you have a dog? My dog likes to pee in a few keys areas almost every time she goes Unfortunately, it's in the lawn and I've got some dead areas because of it that look similar (except they are first straw yellow for a few days and then they lie down matted such as in your photo).

Thats kind of an awkward spot, btw. Is it possible that you have overapplied fertilizer there? I've messed up an awkward spot like that. I did a trim pass with the edge guard on the spreader first. Then when I was doing the main stretch, I didn't stop the spreader soon enough. It would have landed in about the same spot where your troubled area is.

And does that slope face north, south, east, or west?

Where in Ontario are you? More closer to Hudson's Bay or Detroit?

Southern Ontario, no dog. New acquisition, first week of September, not sure what the previous owners did. Also, the entire property is irrigated. It looks so in the picture, but it is completely flat, no slope.