Treasure Chests Don't Spawn

This is the third time in my minecraft realm I went looking for sunken ships, to find maps to treasure chests, and by the time I locate the X on the map, dig all the sand in the surrounding area, (10×10 all the way down to sandstone), I realise that the chest doesn't exist and I've wasted about half an hour on a bug. I would really appreciate you guys looking into this, I just want a heart of the sea.