No. Its only a small lawn and pretty much all the same drainage wise. Never gets too wet although we stay off it in winter. Where the stripe is could be the dryest part of the lawn alright as its across the centre.
As regards an old foundation for a wall there was no sign of one when the soil was dug out and new soil put in before the grass was laid.
If you had a graipe you could test out the depth of any offending material within reason. Anything deeper than the reach of a graipe wouldn’t have much effect on grass quality like that.
A possible suspect might be something leaching from a pipe, like a washing machine sewer line or similar, something like that would really limit the grass quality… but that doesn’t make sense given it would need a fall and would likely be deeper than the effect shown.
I noticed an electrical connection on the right hand side in the first image… is there possibly a cable running across that line? A mother in law is a great pair of hands on the graipe in this scenario. Preferably during heavy rain.
Jab out and peel back a square of it down to a depth of a foot and see what’s there.
Nonsense. I’d say it’s a fairy path.
I’d a hazel or an ash rod, stick one at each end. Wait a few days. If the rods are still standing you’re fine, if they aren’t then, God help you