KeyNotFoundException within NetCode

So I have started a multi-player game and start the client with NetworkManager.Singleton.StartClient(). No big deal. No server is running but after a minute I get this Key not found exception from within NetCode. OK, I know the Dictionary the correct size and it is not checking if the index is out of range. This is not my code so I am assuming that I have missed something in the network setup. What have I missed? The Server is not running so it should not be connected.

KeyNotFoundException: The given key '2' was not present in the dictionary. System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) (at :0) Unity.Netcode.NetworkManager.TransportIdToClientId (System.UInt64 transportId) (at Library/PackageCache/com.unity.netcode.gameobjects@1.0.0-pre.5/Runtime/Core/NetworkManager.cs:1329) Unity.Netcode.NetworkManager.HandleRawTransportPoll (Unity.Netcode.NetworkEvent networkEvent, System.UInt64 clientId, System.ArraySegment`1[T] payload, System.Single receiveTime) (at Library/PackageCache/com.unity.netcode.gameobjects@1.0.0-pre.5/Runtime/Core/NetworkManager.cs:1398) Unity.Netcode.NetworkManager.OnNetworkEarlyUpdate () (at Library/PackageCache/com.unity.netcode.gameobjects@1.0.0-pre.5/Runtime/Core/NetworkManager.cs:1221) Unity.Netcode.NetworkManager.NetworkUpdate (Unity.Netcode.NetworkUpdateStage updateStage) (at Library/PackageCache/com.unity.netcode.gameobjects@1.0.0-pre.5/Runtime/Core/NetworkManager.cs:1196) Unity.Netcode.NetworkUpdateLoop.RunNetworkUpdateStage (Unity.Netcode.NetworkUpdateStage updateStage) (at Library/PackageCache/com.unity.netcode.gameobjects@1.0.0-pre.5/Runtime/Core/NetworkUpdateLoop.cs:149) Unity.Netcode.NetworkUpdateLoop+NetworkEarlyUpdate+<>c.b__0_0 () (at Library/PackageCache/com.unity.netcode.gameobjects@1.0.0-pre.5/Runtime/Core/NetworkUpdateLoop.cs:172)