I have vaadin application with multiple browser tab support. If I launch the application in two separate browser windows directly, it works fine. But when I launch it in embedded iframe in a pop-up window, and do this multiple times, I get this communication problem consistently.
You should grab the stack trace out of your sever log and that can show you where to step through the code in a debugger. Since all of the source code is available, that may be faster than waiting for someone else to try to reproduce this. Then you’ll have a better idea of what the actual problem is to ask about it.
If you’re using maven to build your app, then debugging is even easier – your IDE should just grab the code as needed. I think you’d want to step through the AbstractApplicationServlet#service method, but that’s just an educated guess.