Other than the crazy amount of warning messages, the most probably culprit seems to be the timeout/latency on the steam connection.
LogNet: UNetDriver::TickDispatch: Very long time between ticks. DeltaTime: 0.03, Realtime: 9.83. SteamNetDriver_0
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LogNet:Warning: UNetConnection::Tick: Connection TIMED OUT. Closing connection. Elapsed: 60.02, Real: 60.03, Good: 60.01, DriverTime: 243.45, Threshold: 60.00, [UNetConnection] RemoteAddr: 192.168.0.1:60807, Name: SteamNetConnection_0, Driver: GameNetDriver SteamNetDriver_0, IsServer: YES, PC: FunCombat_PlayerController_C_0, Owner: FunCombat_PlayerController_C_0
LogNet: NetworkFailure: ConnectionTimeout, Error: 'ConnectionTimeout'
LogNet: UNetConnection::Close: [UNetConnection] RemoteAddr: 192.168.0.1:60807, Name: SteamNetConnection_0, Driver: GameNetDriver SteamNetDriver_0, IsServer: YES, PC: FunCombat_PlayerController_C_0, Owner: FunCombat_PlayerController_C_0, Channe...
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