Buried treasure chest not there

so I discovered the shipwreck and got a map with a X and gone there and excavated the whole area to find no chest, it cant be under bedrock so it must not be there. I get another map and oh it the same map but a different X which I thought wasn't possible so I go there excavate the whole area and part of ocean still no chest, i'm started to think this X is either a massive X or in wrong spot I then decide get another map and in the end I have 6 maps and all are the same no chest in a fully excavated area, here are my screenshots of a duplicate map with different treasure locations and a map with no land to excavate lol all other maps are pretty much the same no land around X to dig just ocean.