Individual layers of chunks are suddenly disappearing.

Hey,

also, in the bottom image, you can see this sudden "hole" on a flat surface, which I've circled in red. This particular hole measures 16 by 16 blocks, indicating that it appeared within a single chunk. This has happened to me twice now on my Survival Realm. The issue seems to arise when I flatten large areas. Additionally, before I noticed this hole, I had difficulties joining my Realm. It took an eternity to load, and the connection was eventually dropped. After about 30 minutes of trying, I finally managed to join. That's when I discovered this hole within a chunk.

Update: This bug sometimes occurs when I leave and join the realm.