Placed blocks will disappear, and destroyed blocks will not be dropped. Same thing happens to water and lava, when i place it down, the water/lava disappears and i'm left with the bucket. After disconnecting and reconnecting to the realm, everything placed previously returned to my inventory.
This is happening in realms, in one of the 4 chunks at central spawn chunks, in a small area, where only in that area does this happen. Tried going to nether and end realm, tried to enter through end portal to spawn in the spawn chunks, nothing happened. Also tried to move away from spawn but nothing happened.
In the photo, the bug is happening inside the red box. The blue line indicates the centre of spawn chunks.