End-to-end connection: closed due to problem detected locally, reason code 5003. (Timed out attempting to connect)

Basic listen server using SteamNetworkingSockets results in connection error in 2.0 alpha 2 release. Windows firewall and AV disabled.
Attempts to connect for ~10 seconds and then spews out the following in ConnectionInterface.Connection.DetailedStatus():

End-to-end connection: closed due to problem detected locally, reason code 5003.  (Timed out attempting to connect)
    Current rates:
        Sent:   0.0 pkts/sec   0.0 K/sec
        Recv:   0.0 pkts/sec   0.0 K/sec
        Ping:0ms    Max latency variance: ???ms
        Est avail bandwidth: 128.0KB/s  
        Bytes buffered: 0
    Lifetime stats:
        Totals
            Sent:         23 pkts          11,065 bytes
            Recv:          3 pkts             544 bytes
        No ping distribution available.  (1 samples)
        No connection quality distribution available.  (0 measurement intervals)
        Latency variance histogram not available
        TX Speed histogram: (9 total samples)
             0 - 16 KB/s:    9  100%
            16 - 32 KB/s:    0    0%
            32 - 64 KB/s:    0    0%
           64 - 128 KB/s:    0    0%
          128 - 256 KB/s:    0    0%
          256 - 512 KB/s:    0    0%
         512 - 1024 KB/s:    0    0%
              1024+ KB/s:    0    0%
        Transmit speed distribution:
            50% of speeds <=    0 KB/s
            75% of speeds <=    0 KB/s
        RX Speed histogram: (9 total samples)
             0 - 16 KB/s:    9  100%
            16 - 32 KB/s:    0    0%
            32 - 64 KB/s:    0    0%
           64 - 128 KB/s:    0    0%
          128 - 256 KB/s:    0    0%
          256 - 512 KB/s:    0    0%
         512 - 1024 KB/s:    0    0%
              1024+ KB/s:    0    0%
        Receive speed distribution:
            50% of speeds <=    0 KB/s
            75% of speeds <=    0 KB/s
    No rate stats received from remote host
    No lifetime stats received from remote host

Code:

using UnityEngine;
using Steamworks;
using Steamworks.Data;
using System.Threading.Tasks;

public class NetworkTest : MonoBehaviour
{
    SocketInterface socket = null;
    ConnectionInterface connection = null;

    public void Awake()
    {
        StartServer();
        StartClient();
    }

    public void Update()
    {
        connection?.Receive();
        socket?.Receive();
        SteamServer.RunCallbacks();
        SteamClient.RunCallbacks();
    }

    public void StartServer()
    {
        SteamServerInit serverInit = new SteamServerInit( "SteamNetworkingSockets", "SteamNetworkingSockets test" )
        {
            GamePort = 28015,
            Secure = true,
            QueryPort = 28016,
            VersionString = Application.version
        };

        try
        {
            SteamServer.Init( 480, serverInit );
            SteamServer.LogOnAnonymous();

            socket = SteamNetworkingSockets.CreateNormalSocket<SocketInterface>( NetAddress.AnyIp( 28015 ) );
        }
        catch (System.Exception e)
        {
            // Couldn't init for some reason (dll errors, blocked ports)
            Debug.LogException( e, this );
        }
    }

    public async void StartClient()
    {
        // Wait for server to start
        await Task.Delay( 1000 );

        try
        {
            SteamClient.Init( 480 );

            connection = SteamNetworkingSockets.ConnectNormal<ConnectionInterface>( NetAddress.From( "127.0.0.1", 28015 ) );
            ConnectionStatusAsync();
        }
        catch (System.Exception e)
        {
            // Couldn't init for some reason (steam is closed etc)
            Debug.LogException( e );
        }
    }

    async void ConnectionStatusAsync()
    {
        while(connection != null && !connection.Connected)
        {
            Debug.Log( connection.Connection.DetailedStatus() );
            await Task.Delay( 1000 );
        }
    }

    public void OnDisable()
    {
        connection?.Close();
        connection = null;
        socket?.Close();
        SteamClient.Shutdown();
        SteamServer.Shutdown();
    }
}

Ifdef'ing SERVER and CLIENT separately and running the server in batch mode gives some extra info:

\src\steamnetworkingsockets\clientlib\steamnetworkingsockets_connections.cpp (1816) : Assertion Failed: Application didn't accept or close incoming connection in a reasonable amount of time.  This is probably a bug.
\src\steamnetworkingsockets\clientlib\steamnetworkingsockets_lowlevel.cpp (117) : Assertion Failed: SteamDatagramTransportLock held for 187.8ms!

Facepunch / Facepunch.Steamworks

End-to-end connection: closed due to problem detected locally, reason code 5003. (Timed out attempting to connect) #268