JSON call from server application


We have a problem when calling an application with a JSON call.
I hope someone in this forum can give me a hint on what to do.

We have a server application accessed via a web browser. In the application, we have a button that generates a JSON content and sends the JSON call to another system. The other system should open up in a new tab in the web browser, and it does, but in 75% of the cases it does not show the sent data. In 25% of the cases it does.
We have figured out that the sending system is creating two calls, one from the server side and one from the browser client.
The receiving system (4 servers) are behind a load balancer and we can see that its working when both the server call and client call is routed to the same server, if not we get the unwanted behavior.
We are using single sign on, so the user that press the buttons access rights is allowing or blocking the call. This works fine.

Do you have any idea what we are doing wrong?

Can we get the system to just send one call from the client?

All ideas are very much appreciated.