Location was bugging me especially in relation to SE stone wall - stony ground but no other boulder clusters. So I think Brendan's diagnosis is right - incorrectly mapped too high.
But when you approached from the downhill swamp side, you could see the flag from far enough away that your brain moves on to the next control... maybe I just got lucky. I noted the stone walls but didn't try to use them to attack.
On balance you executed just fine-saw you in the distance and made a conscious decision not to converge, however my GPS track suggests I was offline.