Half my world disappeared while active

Half of my builds were destroyed once I came back into render distance. I hadn’t existed the app for about 30 minutes and want to know if anyone has had this issue and was able to recover their builds. I spent numerous hours on the builds just for the world to disappear before me. I’ve been playing mc for years and have never had this issue so I’m very confused. In the picture is the before and after of how my world looked like.