The processor is working under its specifications. Turbo Boost increases the Core speed; however, only 1 Core will reach the maximum, in this case 4.2Mhz the rest will run slower.
The picture below shows expect Core speed on 6th gen processors
Further information about Intel® Turbo Boost Technology at
On my processor, I observe each core reaching 42x, but it really doesn't matter for the sake of this argument
This specific processor doesn't reach 42x ever, the performance blocking flags I mentioned gets set, it stays at 40x, my brother also reported glitches during usage, disabling Turbo fixed the issue, the flags no longer get set
Folks who know more pointed out that it's most porbably a BIOS/voltage issue that might get solved: Overclockers Forums
I'm just wondering whether it's a faulty CPU