20 is worse than 18 threads? what's wrong?

[Rid Streenger]

There is a strange problem - the same test when choosing 18 cores shows the result almost 10% higher than with 20 cores.
We ran more than once sequentially one after another, in a different order. The result does not change.
https://1.downloader.disk.yandex.ru/preview/044fc76323264cd8d08e3c9ee2846fde5fa7824d4103575e9c 5f801b878a5301/inf/oXObQsOZ3585FKr-1Sg08AfM26XZCsRE7H2WCqxFbInef6LPIXOfrMH7R8pPrA7zof zlj0JfhKJMmL4hNUS4UQ%3D%3D?uid=1130000037958213&filename=cpuz.jpg&disposition=inline&hash=&limit=0&content_type=image%2Fjpeg&owner_uid=1130000037958213&tknv=v2&size=1903x969
Who can tell you what the problem is and how to fix it?

https://valid.x86.fr/cache/banner/juwa39-2.png (https://valid.x86.fr/juwa39)

[111aaa]

Maybe its due to the different clock speed?

[Rid Streenger]

No, the clock frequency does not change in both cases. Also, this is not related to parked kernels (I fixed the registry, rebooted the computer) Moreover, I launched two applications and sequentially ran the test with 18 and 20 threads - the difference is visible.

https://a.radikal.ru/a27/2104/40/96dac846314a.jpg