Windows Zero Condition, App or Client

I am using Wireshark 2.0 to try and determine a problem on that a few of my users are experiencing. The client computers are connecting to a database server via an application installed on the client computer. What is happening is that clients that are connecting to the server are seeing a delay on the files that the application should be downloading. What previously took a few seconds is not taking a couple minutes. I’ve noticed on every client computer that I performed a capture on a TCP ZeroWindow event being sent from the client computer to the server. I’ve also captured the three-way handshake between client and server the the window size on both sides is set to 8192 with windows scaling enabled and a multiple of 256, this is plenty of buffer space. Yet the client computers all have the same condition, they get data from the server but eventually run out of buffer space and announce to the server that the window size is 0. I ran ftp on the clients and did not experience the same thing. To me this is looking more like the application on the clients is not getting the data fast enough from the buffer and causing the clients window size to get full. Any help would be appreciated.