For example if you join to a realm server and you want to build something, you will see that your building looks normal, but usually, when you rejoin in the same server, you will see that some blocks didnt get saved, some parts of the building are missing.

To prevent this bug firstly i place a block, and then i mine it, if the item drops, its ok, but if the item doesnt drop, i have to reconnect to the realm server.