For years we have successfully used the WebBrowser IE control to display numerous different webpages, many (nearly 50%) of which deploy a lot of their content using Flash.
However, as customers update to having IE11 installed on their system we find that Flash becomes flaky at best. On some computers with the same software installed one flash-based site will work and another will not. Or, the first time you visit the site it will work but if you navigate away from the site and then revisit the site you will never be able to get the Flash content to load again (including after system restarts).
On one system I had several sites that were not working. I then ran as Administrator and all of a sudden those sites started to work again but several of the flash sites that HAD been working could no longer display any of the flash content.
The issues do not exist with any other version of IE installed, just IE11.
A sample of sites where we have had this issue includes:
http://www.storylineonline.net/
http://video.nationalgeographic.com/video/kids/animals-pets-kids/
http://www.speakaboos.com/
http://www.schooltube.com/
This never seems to be an issue when using IE11, just when using the WebBrowser control when IE11 is installed.
I apologize that I cannot provide more specific replication steps, but it seems fairly random as to when a site will work vs stop working. Generally speaking once a site stops working we have been unable to find a way to get it to start working again.