I have a similar problem, i played around 22h with a friend.
But if we start the game, the client gets disconnected after 1-2min with a "Outgoing reliable buffer overflow".
Singleplayer works fine, but impossible in coop
[2020.01.01-18.46.25:044][207]LogConveyorNetDelta: Warning: CR:124:Build_ConveyorBeltMk3_C_126:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: 125. Recived: -104 to -103, diff: 27.
[2020.01.01-18.46.25:045][207]LogStreaming: Display: Flushing async loaders.
[2020.01.01-18.46.25:045][207]LogConveyorNetDelta: Warning: CR:1332:Build_ConveyorLiftMk3_C_8:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: -85. Recived: -52 to -51, diff: 33.
[2020.01.01-18.46.25:045][207]LogConveyorNetDelta: Warning: CR:1319:Build_ConveyorLiftMk3_C_7:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: -120. Recived: -102 to -101, diff: 18.
[2020.01.01-18.46.25:050][207]LogConveyorNetDelta: Warning: CR:1184:Build_ConveyorBeltMk3_C_1234:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: 73. Recived: 101 to 102, diff: 28.
[2020.01.01-18.46.25:050][207]LogConveyorNetDelta: Warning: CR:192:Build_ConveyorBeltMk3_C_199:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: 79. Recived: 107 to 108, diff: 28.
[2020.01.01-18.46.25:050][207]LogConveyorNetDelta: Warning: CR:1055:Build_ConveyorBeltMk3_C_1104:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: 75. Recived: 104 to 105, diff: 29.
[2020.01.01-18.46.25:050][207]LogConveyorNetDelta: Warning: CR:1045:Build_ConveyorBeltMk3_C_1094:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: 52. Recived: 71 to 72, diff: 19.
[2020.01.01-18.46.25:050][207]LogConveyorNetDelta: Warning: CR:799:Build_ConveyorBeltMk3_C_839:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: 57. Recived: 75 to 76, diff: 18.
[2020.01.01-18.46.25:050][207]LogConveyorNetDelta: Warning: CR:1254:Build_ConveyorLiftMk3_C_3:+Out of order package/dropped package... Skipping and waiting for suitable package. Current version: 79. Recived: 111 to 112, diff: 32.
[2020.01.01-18.46.25:050][207]LogNet: Warning: Network Failure: GameNetDriver[FailureReceived]: Outgoing reliable buffer overflow
[2020.01.01-18.46.25:050][207]LogGame: Error: Network Error Recived: Type: 1539520064, MSG: Outgoing reliable buffer overflow
[2020.01.01-18.46.25:050][207]LogNet: NetworkFailure: FailureReceived, Error: 'Outgoing reliable buffer overflow'
[2020.01.01-18.46.25:050][207]LogNet: UNetConnection::Close: [UNetConnection] RemoteAddr: EG.0b1f7589d0d24d099dc5f51f5001cd866b86a00d42c145b8bb17faa1a0749c71:7777, Name: EpicNetConnection_0, Driver: GameNetDriver EpicNetDriver_0, IsServer: NO, PC: BP_PlayerController_C_0, Owner: BP_PlayerController_C_0, UniqueId: Mcp:78a6f7c0c2a44871a1f3030addfcf1bb, Channels: 4372, Time: 2020.01.01-18.46.25
[2020.01.01-18.46.25:050][207]LogNet: UChannel::Close: Sending CloseBunch. ChIndex == 0. Name: [UChannel] ChIndex: 0, Closing: 0 [UNetConnection] RemoteAddr: EG.0b1f7589d0d24d099dc5f51f5001cd866b86a00d42c145b8bb17faa1a0749c71:7777, Name: EpicNetConnection_0, Driver: GameNetDriver EpicNetDriver_0, IsServer: NO, PC: BP_PlayerController_C_0, Owner: BP_PlayerController_C_0, UniqueId: Mcp:78a6f7c0c2a44871a1f3030addfcf1bb
[2020.01.01-18.46.25:050][207]LogNet: Warning: Network Failure: GameNetDriver[ConnectionLost]: Your connection to the host has been lost.
[2020.01.01-18.46.25:051][207]LogGame: Error: Network Error Recived: Type: 1539519992, MSG: Your connection to the host has been lost.
[2020.01.01-18.46.25:051][207]LogNet: NetworkFailure: ConnectionLost, Error: 'Your connection to the host has been lost.'