We use StackExchange.Redis in SignalR Redis scale-out, I found after Redis restart in ConnectionRestored event sometimes ConnectionMultiplexer.IsConnected is False, we need reading Redis Key in ConnectionRestored event handler, in this case it throw RedisConnectionException.

Here is simple repro app:

       private static ConnectionMultiplexer _connection;
        static void Main(string[] args)
        {
           string connectionString = "......";
            _connection = ConnectionMultiplexer.Connect(connectionString);

            _connection.ConnectionRestored += OnConnectionRestored;

            Console.ReadLine();
        }

        private static void OnConnectionRestored(object sender, ConnectionFailedEventArgs args)
        {
            Console.WriteLine("_connection.IsConnected is " + _connection.IsConnected);
        }

Repro steps:
1). Update connectionString for your Redis, build the app and run
2). Stop and Restart the Redis, look the console output, repeat this step until in output see: _connection.IsConnected is False

Expected result:
in output it always should display "_connection.IsConnected is True" after Redis restart

Actual result:
On my machine, after I restart Redis about 3 times, I can see " _connection.IsConnected is False" in output.