CPU inconsistently thermal throttling

[AJAY_456]

Just moved my system into an ITX case. Motherboard and graphics card changed but 3700x staying the same. No issues in my old case.

Now, when I first boot up the cpu immediately thermal throttles normally around 90 degrees and will slowly increase if I let it all while sitting idle. I turn it off and immediately turn it back on again, and the cpu then sits at 35/40 degrees. I can then go and play games without it exceeding 50. 

Anybody know why on the first boot up it might be doing this? 

[Bismut]

It sounds like a sensor or driver issue, like the CPU temp is not read correctly or it gets OCed accidentally on first boot? It is very odd, I'm interested to see what others have to say.