My friends and started a realm after the Nether Update and on all devices (Windows 10, Xbox One, Android) any treasure maps found in shipwrecks or underwater ruins all point to the same chest that was already discovered. We even tested it by going out over 16,000 blocks and this was still the case. I am not sure if this is an issue with the maps or if the world did not generate any other hidden chests. No one has found one by chance, the only chest found was the one where every map points. The maps function like normal when we get close to the X i.e. the maps start uncovering. The hidden chest that was found appeared to have generated normally. I have not tried to test this with any other worlds/realms.