I'm having exactly the same experience. I can set everything the same in Intel XTU, let the machine rest for 5 minutes and then start the game and have completely different framerates each time. Even during a single round the game goes down to 10 to 15 fps for a minute and then suddenly goes back to 60 fps for 5 minutes.
It's almost certainly due to throttling of the GPU, but I set my CPU to be as low as 15 Watts with multipliers in the 20's, so the Macbook should be able to cool it in that situation right? The GPU also starts throttling even though its temperature is 65-70 degrees, not sure what are high temps for a GPU, but 70 degrees doesn't seem so high?
Edit:
So right now my settings:
- Bootcamp, Windows 10 Pro, Powermode: Best performance
- Windows power management for cpu : 99%
- Intel Xtu: 15 Watts, disabled Turbo Power max
- Multipliers at 24x (changing them lower or up doesn't seem to make a difference on whether or not the GPU is throttling.)
- Device is fully charged and plugged in.
Outcome
- The CPU is at 68 Celsius, pulling in around 12-14 Watts. No thermal throttling
- After 2 minutes the GPU starts throttling down to 303Mhz and then further down to 213.
- GPU memory used around 2400mb
- GPU 63 degrees, GPU only power draw 10 to 23 Watts.
This is with the fans fully on using the application on MacOs and then restarting. But doesn't seem to make a difference.