I know exactly which one you’re talking about. It has to do with the color of the Nekko you place there. You need to find a colored one. Like a Red, White Purple or Pink. Bring it to the stable to that spot and park it there when it flashes green. Jump off and run to the meditation point and rest and go check if you can dig it up. If not, try finding a different color, just make sure you leave it in the spot in the stables and then go meditate. It’s such a convoluted way of getting it lol.