I wrote a long article explaing how I identified the bug by testing Turbo Boost, CPU temperature, CPU frequency, etc. https://haypo.github.io/intel-cpus-part2.html

Copy/paste of my conclusion:

To get stable benchmarks, the safest fix for all these issues is probably to set the CPU frequency of the CPUs used by benchmarks to the minimum. It seems like nothing can reduce the frequency of a CPU below its minimum.

When running benchmarks, raw timings and CPU performance don't matter. Only comparisons between benchmark results and stable performances matter.

Victor