Adding a few comments for clarification.

Assets/Scripts/Relay/RelayUtpClient.cs

             OnUpdate();
         }
 
+        /// <summary>
+        /// Clients need to send any data over UTP periodically, or else Relay will remove them from the allocation.
+        /// </summary>
-            // Clients need to send any data over UTP periodically, or else the connection will timeout.
-            if (!m_IsRelayConnected) // However, if disconnected from Relay for some reason, we want the connection to timeout.
+            if (!m_IsRelayConnected) // If disconnected from Relay for some reason, we *want* this client to timeout.
                 return;
             foreach (NetworkConnection connection in m_connections)
                 WriteByte(m_networkDriver, connection, "0", MsgType.Ping, 0); // The ID doesn't matter here, so send a minimal number of bytes.
         public virtual void Leave()
         {
             foreach (NetworkConnection connection in m_connections)
-                WriteByte(m_networkDriver, connection, m_localUser.ID, MsgType.PlayerDisconnect, 0); // If the client breaks the connection, the host might still maintain it, so message instead.
+                // If the client calls Disconnect, the host might not become aware right away (depending on when the PubSub messages get pumped), so send a message over UTP instead.
+                WriteByte(m_networkDriver, connection, m_localUser.ID, MsgType.PlayerDisconnect, 0);
             m_localLobby.RelayServer = null;
         }
     }

Assets/Scripts/Relay/RelayUtpHost.cs

 
         protected override void OnUpdate()
         {
-            if (!m_IsRelayConnected) // If Relay was disconnected somehow, stop taking actions that will keep the lobby alive.
+            if (!m_IsRelayConnected) // If Relay was disconnected somehow, stop taking actions that will keep the allocation alive.
                 return;
             base.OnUpdate();
             UpdateConnections();
         public override void Leave()
         {
             foreach (NetworkConnection connection in m_connections)
-                connection.Disconnect(m_networkDriver);
+                connection.Disconnect(m_networkDriver); // Note that Lobby won't receive the disconnect immediately, so its auto-disconnect takes 30-40s, if needed.
             m_localLobby.RelayServer = null;
         }
     }