This happened when I opened a YouTube link in a tweet, and then after watching the video I tapped a link to a related video. The page started loading, and I got the UI, and then while the page was fetching related videos, etc. (and the video itself), the UI became unresponsive. I tried tapping the back arrow to get out of the page, and some seconds later the app crashed.
This does not seem to reproduce easily. I tried loading the same YouTube page and do the exact same, but it didn't crash that time.