@@AZOR6339 I think you need to press the 2 buttons [Play and Multiplayer] at same time, if you got the select map from "Play" select a map or a saved map and then you will have a free sandbox map
As a small dev myself I don't know what to call this bug I first thinked of internet bug of that player Or the system stop all (but the stop all bug cant be in unity "I think idk") Idk what to call it but if the player is talking and others see him move but you don't its probably bad connection or something idk how to explane it