How to reproduce:
1. Open attached project
2. Load StartMenu scene
3. Enter Play Mode
4. Click Join LAN Game
5. Observe Console

Expected result: Error 'Client failed to connect to server' and popup in-game
Actual result: KeyNotFoundException in Console and no in-game popup

Error:
Failed to connect to server.
UnityEngine.Debug:LogError (object)
Unity.Netcode.UnityTransport:ProcessEvent () (at Library/PackageCache/com.unity.netcode.adapter.utp@1.0.0-pre.6/Runtime/UnityTransport.cs:659)
Unity.Netcode.UnityTransport:Update () (at Library/PackageCache/com.unity.netcode.adapter.utp@1.0.0-pre.6/Runtime/UnityTransport.cs:699)

KeyNotFoundException: The given key '4294967296' was not present in the dictionary.
System.Collections.Generic.Dictionary`2\[TKey,TValue].get_Item (TKey key) (at <5c11b4a72acd40aeb3dee4e6d69cca92>:0)
Unity.Netcode.NetworkManager.TransportIdToClientId (System.UInt64 transportId) (at Library/PackageCache/com.unity.netcode.gameobjects@1.0.0-pre.6/Runtime/Core/NetworkManager.cs:1340)

Reproduced with: 2022.1.0b12, 1.0.0-pre.6
Does not reproduce with: 1.0.0-pre.5