Forza Horizon 4 - FPS problem

Hi! I have a big problem running Forza Horizon 4 on my PC:

The game runs perfectly fine on “high/ultra” settings but after 15/30 minutes of gameplay it starts stuttering (frame rate drops). Settings actually don’t make any difference, even on the settings that game sets it’s still the same.
Don’t know what to do with this, I need to restart the game every time this happens and it’s fine again for 15 or 30 minutes.
I should be able to play the game on high settings easly, the fps is over 80, temperatures are super low, nothing is wrong.

My PC specs:
I5 8400
8GB DDR4 2400

A moderator from the Windows forum gaves me this solution to try: troubleshooting steps, but unfortunately doesn’t work for me. At first I was thinking that works, but then two nights ago I was playing and stills again the same issue. It’s so frustrating, the game runs perfectly and suddenly the frame rate starts to fall and the game starts stuttering.
I read about people having the same issue (and a better pc specs than me!), but I can’t find any solution. And just for you to know I always play the game in the offline mode.

Do you have any reccomendation on how to fix this problem? Thank you!