Here's something to try: in the project that gets frozen, append to a text object whenever 'On suspended' or 'On resumed' triggers in the Browser object. It might be pausing because iOS is firing a 'page hidden' event, which causes the game engine to pause, and then fires a 'page shown' event when you interact with it. Unfortunately this would only confirm it's an iOS bug, because it shouldn't send a 'page hidden' event when you can see the page!