This is a problem I've been noticing since the youtube embed design change, at least from what I've noticed.
So what's happening is any web pages that have been added to homescreen that have a youtube video embedded will autoplay the first youtube video on screen in the youtube app. This doesn't happen when you open the same web page is opened in safari.
Basically any web pages that have a youtube video embedded are inaccessible due to it automatically redirecting you to the youtube app.
How can I stop this? Or is it something they've added that can't be fixed?