You are calling open level on the client side… So what you are doing is basicly having the client open the level. The server is not switching levels its just the local client that is switching levels. That is why when both press K they are not in the same level because they are no longer on the dedicated server as they both opened local levels on there local client. Thats also why when you do a open 127.0.0.1 it connects back to the server and then after both clients have done this they are on the same level.
What you can try doing is making a function that executes on the server and then put the command to open the level you want. Then have it when you press K it calls that server side function.
I tried to do the function in game mode that should be only on server
