Question Spontaneous problem with CPU fan after wake up ?

Nov 24, 2022
So I woke my pc up after sleep the way I do quite often but this time the cpu fan came on and stuck at 100%
Restarted the pc and it settled down until I was back on the desktop for 10 seconds then it stuck at 100% again.
Restarted again and this time it was full speed even at post. Went into bios and disabled Q-fan control and also tried fiddling there to set the speed lower to no avail. Also tried optimised defaults.
Went back into windows and used speed fan to bring it down to 40% and it stayed there for 10 seconds then went back to full speed. Then I tried again but nothing happened. It seems I have to play with it a few times before speed fan can override it but it only works for 10 seconds then whatever is the cause kicks back in again.

I'd like to know a few things before i open the pc up:
Does the fact speedfan works (temporarily) mean the pwm controller is OK?
What are the possible culprits giving that the problem also occurs outside of windows?

I think it has to be a hardware problem or corrupt bios but I've never had that problem before.

Will wait for some feedback before I proceed.

Specs : (old I know)
Cpu - AMD FX8150
Motherboard - Asus sabertooth 990fx rev 2.0
Cooler - hyper212 with 1x stock fan and 1x corsair sp120 through a splitter because for some reason 2x sp120 wouldn't work with pwm when I built it but mixing them with a splitter worked.
Anyway that was 10 years ago so don't think it would be the issue now. I've had some mileage out of this and still play the latest games with high+ settings but need a little more time!