I just updated Safari to 10.0 this AM and as soon as the system had restarted, the screen saver did not launch as it always does after 10 min of inactivity. I restarted again and it did not correct the problem. I'm using OS X 10.11.6 on an iMac. I use "Moments" as a screen saver.
iMac, OS X El Capitan (10.11.6), Safari 10.0