Oh also when in fullscreen and tabbing out while joined to a server will make you disconnect. But only when in fullscreen, maximized window and windowed mode works fine
That is not a bug. It is a feature of the game
That is a chunk error. It happens sometimes in the game.
The level.dat file is in the photo. You can access it by using NBTExplorer https://www.minecraftforum.net/forums/mapping-and-modding-java-edition/minecraft-tools/1262665-nbtexplorer-nbt-editor-for-windows-and-mac.
reminds me of the thing i am not sure if it's a bug or intended, where you can't stop a hopper if it's above a different hopper by directing a redstone signal into it