The issue I had was that in IE (and Firefox if I'm not mistaken), the browser was taking too long to start streaming and, before it did, a popup saying something like "Unable to find engine".

The issue was because we set it up asynchronously in a bad manner. It was trying to create a more than one engine when more than one topic was being streamed in the same page. Somehow, Chrome handles it and IE not always has this issue and so I had missed it at first.

It is troubling to find such a message and not know where it came from as the stacktrace is completely useless when the code is minified so aggressively.

Thanks