Extremely low FPS (Assassin's Creed: Origins)

Good day!
I have a problem from the category of the mystical.
When you start the game in 80% of cases the game gives 8-20 Fps.
In the other 20% safely held at 50-70 Fps.
Yesterday, after 15 minutes of the game the fps dropped from 50 to 10 and doesn't get up.
With all these pies CPU video card does not rise above 50%, free RAM remains about 300 MGB (for monitoring GPU Z).
CPU utilization rises above 40%, and RAM is not above 50% (according to task Manager).
Hardware configuration:
Intel Core I7 860 2.8 MHz
16 gigabytes of RAM
Hard drive SSD 250 Gb
The GeForce GTX 1060 3Gb
Latest video driver with Geforce Experience
Windows 10 (this week updated)