Basicly after i start server and spawn all my moving platforms, if client is not logged in and he logs in abit later after spawning moving platforms, then each player has his own moving platforms, server’s is farther in progress and they are not synced at all. That also causes dissapearing for each other, while on moving platform. Huge help would be, if anyone would help me understand,how to get that progress, where is moving platform currently when i login with client, when all moving platforms were already spawned like 5 seconds before me. So when i login there wont be new platform for me from beginning, but already in progress of server’s platform 
Thx in advance.
This should be solved by placing NetworkViews on each of the platforms, and telling the component to observe the transform component (which is done by default).
Now you would only want the server to move the platforms, and the network views make sure that the position is updated on all clients. This can be achieved by checking the bool networkView.isMine. This is true if this is the client that spawned the platforms (only works if Network.Instantiate is used).
This should fix the problem, or alternatively you can use a RPC to send the current position of the platform to the connecting client, and use this data (Vector3) to synchronize them. OnSerializeNetworkView could also help: Unity - Scripting API: Network.OnSerializeNetworkView(BitStream,NetworkMessageInfo)