The problem is that the inventory from the hotbar doesn´t get saved, there will be problems, like for example, guests players selecting nothing in the hotbar and the client player would see another block.

How to reproduce the bug:
1.-Join to a server
2.-Select something from the inventory to be moved to the hotbar (ex: sword)
3.-You will see that the sword will be in the hotbar
4.-Disconnect from the world
5.-Rejoin in that server
6.-The hotbar will be cleared.
7.-You will see that the box selected from the hotbar will be empty, BUT the client player will see the guest with the sword in their hand.
8.-If the guest hit the client player, this will receive a damage like the sword.