For a couple of weeks I had a problem where YouTube playback stopped, and the video player would only display a spinning circle.
It turns out that this is a bug with the video player when Hardware Acceleration is enabled in Chrome (and possibly other browsers).
To turn off hardware acceleration, go to Menu --> Settings --> Advanced.
In the "System" section, find "Use hardware acceleration when available" and turn it off.
Seems to have fixed the problem for me so far, at the cost of higher CPU load.