Adding entrances/exits doesn't work at all, they delete immediately. When placing a station, the server would place another station tile in front of it that the client can't see. When you delete the station the client placed, the client would then see the new station on the server. If the client builds tracks from either station, it doesn't sync up to the server and stays only on the client end. At first we thought this was because of added mods, but even after drilling it back down to just multiplayer and starting on fresh saves we'd run into the same problem frequently/consistently. It's also worth noting that each new ride entrance placed by the clients disappeared immediately but still spawned a ride operator on the server end.