Hi, just created an account to report this issue when I stumbled on this post. I experience the same problem, here's the report I originally typed
Sometimes, opening a Youtube video and clicking fullscreen (or pressing F) will freeze the page. Nothing will move, scroll, keyboard and mouse are unresponsive in the tab, but audio will keep playing. Others tabs are unaffected and closing the tab is quick.
This doesn't happen every time (once every 10-20 videos approx.), and seems unrelated to whether or not the system is overloaded (there is plenty of CPU and memory left.)
Unfortunately, I haven't found a way to replicate this
I have no extensions installed, running on a Macbook Pro 2,6 GHz 6 core i7, Radeon Pro 560X 4 GB, and running a 49" monitor as my only display (clamshell mode).
EDIT: refreshing the page doesn't work, the screen stays frozen, I have to close it and re-open the link in a new tab