Thank you for sending us the complete code.
The main issue was that args.Message.ApplicationName.ToString(); raised NullReferenceException on a background task, which stopped execution of the foreach (var args in messageQueue.GetConsumingEnumerable()) loop.
Please note that string properties of the args.Message can be null if the client did not send their value.
I also suggest to put body of the message processing foreach loop into try-catch block and handle errors appropriately.