The issue occurs because, when the communication between two servers that use Service Broker, database mirroring or Availability Groups occurs, the window size of TCP protocol does not expand automatically. TCP window size determines the number of bytes that a sender can transmit without receiving an acknowledgement. When the client is receiving data from SQL Server database, the client holds a constant TCP window size. After large amount of data is sent from SQL Server database, the window size on the client will gradually come down to 0. Therefore, the connection to SQL Server database makes high latency and the response takes much more time.