The issues on disaplay are:
Duplication on StopHost
The Unity Networking system is creating a new instance of the LobbyManager (inherits NetworkLobbyManager.cs)
Am I supposed to Destroy the lobby object here, and why?
UI elements misplaced on Canvas
This issue appears when a new LobbyPlayer is spawned and then parented the slot. Notice how it works fine on the host, but is misplaced on the clients.
(A simple fix to this is to set the transform.localPosition of the LobbyPlayer to Vector3.zero on start, but that is a hack and it should be working in the first place.)