If you are using Azure SQL Database you may occasionally experience following exception (this is example throw by native SqlClient library):
System.Data.SqlClient.SqlException: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. This failure occurred while attempting to connect to the routing destination.
What is this? Azure system may occasionally quickly shift hardware resources to better load-balance various workloads. During this reconfiguration time span, you may have connectivity issues to Azure SQL Database.