Buried treasures may not contain items if there're other treasure cases. Temporarily I don't know how to reproduce that, so I just say it "may not".

This situation happened at least 3 times in my server these days, I can promise that nobody came here except me, because these chunks were new. The only thing in common that I know is, there're other treasure cases near these burried treasures, such as village cases, shipwreck cases or another burried treasure case.