We have a Flex application (yes, we are working on a rewrite outside of Flex) that started randomly freezing up the browser (IE11) after updating to Flash Player 28. I haven't found any references to this on the net, wanted to see if it's a known issue and if so what the solution would be. Our back-end is Coldfusion 2016.
Nothing that I'm aware of. Have you tried using the ActionScript debugger? It might give you something interesting.
Alternatively, if you have a link and steps to reproduce the issue, I'd be happy to have someone take a look.