My friend has the exact same error(s) when im already connected. If you need both full log files (or update to date ones) let me know.
factorio-current.log
10053.482664 Notice Router.cpp:77: Joining game xxx.xxx.xxx.xxx:34197 at port 34197
10053.482678 Info WindowsUDPSocket.cpp:55: Opening socket at port (34197)
10053.482730 Info Router.cpp:372: Router state -> Connecting
10053.483031 Info MultiplayerManager.cpp:470: networkTick(0) mapTick(-1) changing state from(Disconnected) to(Connecting)
10053.499493 Info Router.cpp:372: Router state -> WaitingForAccept
10053.562548 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563236 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563265 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563283 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563300 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563317 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563335 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.568874 Info Synchronizer.cpp:59: NetworkTick(19580) initialized Synchronizer local peer(2).
10053.568941 Info Router.cpp:372: Router state -> Connected
10053.569012 Info Router.cpp:492: Own peer id is 2
10053.569045 Info MultiplayerManager.cpp:470: networkTick(19580) mapTick(-1) changing state from(Connecting) to(VerifyingConnection)
10064.010386 Info MultiplayerManager.cpp:470: networkTick(19580) mapTick(-1) changing state from(VerifyingConnection) to(Failed)
10070.115876 Info MultiplayerManager.cpp:84: NetworkTick(19580) quitting multiplayer connection.
10070.115936 Info MultiplayerManager.cpp:470: networkTick(19580) mapTick(-1) changing state from(Failed) to(Disconnected)
10070.134567 Info WindowsUDPSocket.cpp:108: Socket closed
10070.134621 Info Router.cpp:372: Router state -> Disconnected
10882.376812 Info GlobalContext.cpp:470: Goodbye
10053.482678 Info WindowsUDPSocket.cpp:55: Opening socket at port (34197)
10053.482730 Info Router.cpp:372: Router state -> Connecting
10053.483031 Info MultiplayerManager.cpp:470: networkTick(0) mapTick(-1) changing state from(Disconnected) to(Connecting)
10053.499493 Info Router.cpp:372: Router state -> WaitingForAccept
10053.562548 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563236 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563265 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563283 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563300 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563317 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.563335 Info Router.cpp:272: Received packet with invalid session magic 53999 from xxx.xxx.xxx.xxx:34197
10053.568874 Info Synchronizer.cpp:59: NetworkTick(19580) initialized Synchronizer local peer(2).
10053.568941 Info Router.cpp:372: Router state -> Connected
10053.569012 Info Router.cpp:492: Own peer id is 2
10053.569045 Info MultiplayerManager.cpp:470: networkTick(19580) mapTick(-1) changing state from(Connecting) to(VerifyingConnection)
10064.010386 Info MultiplayerManager.cpp:470: networkTick(19580) mapTick(-1) changing state from(VerifyingConnection) to(Failed)
10070.115876 Info MultiplayerManager.cpp:84: NetworkTick(19580) quitting multiplayer connection.
10070.115936 Info MultiplayerManager.cpp:470: networkTick(19580) mapTick(-1) changing state from(Failed) to(Disconnected)
10070.134567 Info WindowsUDPSocket.cpp:108: Socket closed
10070.134621 Info Router.cpp:372: Router state -> Disconnected
10882.376812 Info GlobalContext.cpp:470: Goodbye