OovooJaver

Hello, I have a small server which i play with 2 of my friends. We've built quite a number of houses and farms, its been up for about 2 months and we've really been enjoying ourselves. Recently I noticed that one of my houses got absolutely destroyed and the pieces missing were along chunk borders. For instance one of the missing parts in my houses was filled by a copy of a chunk of a mountain side right next to it, pic is below. I don't know if its reversible but I'm just scared that it happens again and I don't know how to avoid it. There was a lot of valuable loot in that houses along with many shulker boxes which were a pain to get. Could I get some advice?