GPU throttling on MBP 15 2017

Hello! I have a problem Radeon 555 on my Apple MacBook Pro 15 with Retina display Mid 2017 256gb.

Running on Windows 10 build 1803. (Clear Installed in May)

The cooling system operates correctly 5900rpm on the left and 5500rpm on the right
I make reset SMC.

I love play FIFA 18 on my notebook. 11 months I played without problems (60fps ultra graphics). Then began to appear small lags (small drops to 53 fps).

Now instead of 60 fps I get 25-30 fps.. I decided to test my computer with programs Fumark and GPU Shark.
CPU load 1%-2%

1 min stress-test

2 min stress-test

4 min – freq down to 693mhz

4:20 min - freq down to 590 mhz

12 min - end stress-test. AVG freq 693mhz (sometimes down to 590 and up to 782 mhz)

Stress-Test with CPU load 57%

freq 487 mhz ⚠

So I did a test in the Cinebench R15.

96 fps when the macbook is cold

64 fps when the macbook is hot (5 consecutive Tests)

On Mac OS

83 fps when the macbook is cold

73 fps when the macbook is hot (5 consecutive Tests)

(forgot screenshot)

All screens in full resolution – https://cloud.mail.ru/public/GFjs/4DfG5G3Nu

MacBook purchased on August 8 2017

Should I contact the service center? Why is such a fall performance?

PS

I'm from Russia, sry for my English %)