Never enabled Hyper-V.
Tried to run HWiNFO32 instead of HWiNFO64 - the same result (no second CPU).
Uninstalled KB3042085 and KB2976978, disabled all antiviruses/HIPS, restarted system, - nothing changed.
Rollbacked the whole system (have an old back-up image) - the issue disappeared (HWiNFO64...