I bought two M720q i5-8400t and the fan on those are operating normally, i.e. they spin up to 1900-2000rpm if I stress the CPU with say OCCT.
This third unit is M720q i5-8500t and I have no idea what is wrong. The firmware is one version back from the earlier two.
The fan remains at around 1200rpm when I stress it the same way and it's hitting 85-90c with thermal throttling.
Once in a while the fan would spin up to 6000rpm for 5 seconds.
I swapped fans from the 8400t pair and it's the same symptom. All units are undervolted by 125-160mv and whether that is turned on or off, it does not affect this behavior.
Fresh paste on all 3 units.
I'm a bit loss now. It's a motherboard issue?