2 chunks missing to void and not saving builds between saves.

Basically the first issue was the two gaping holes in the ocean. There was one that literally appeared underneath me while boating and when I got out to look, there was a chunk's worth of blocks missing that lead to the void and another chunk missing a couple chunks over. This happened after we have been experiencing a weird bug where things don't save based on what xbox we use (2 different houses). We had made a substantial amount of progress building, only to find it missing when we logged into the other xbox. We started making sure to check the saves before exiting, but it continued to happen. I have built the same house like 3 times, y'all.