In every place with buried treasures by Japanese, vaults are scattered not far away from each other but with varying depths. In this case the magnetic fields of every vault are creating strong magnetic pulling effect to any kind of gadget. At the center of the area with vaults scattered around, magnetic fields of every vault crosses, that spot is what expert called false positive.
Your problem here is not about your gadget because any kind of instrument you are using will just fall victim to the portion of the ground where the false positive spot is located.
Try digging at that spot where your gadget is pointing and you'll find signs and all but signs and then continue your digging and try to reach the depth indicated in the result of scanner, you'll see that depth level has no treasure in it.
This kind of treasure site is very common and that is what i call main vaults cluster. In some few areas as what other expert says there is at least one shallow small cache separated but is quite rare. Most common are main vault cluster without small cache. The shallowest vault in a cluster is at 35 feet.
