Huge lag after Windows 10 start CPU overclocked

[Kaluditz]

What happened: Upgraded PC parts from i5-4670k,Asus Z87-A and ddr3 ram to i5-8600k, Asus Z370 and TridentZ ddr4 ram. I have Windows on SSD and I did a fresh install about 2 weeks ago.

So when i first got the PC running after installing new parts and drivers all worked like normal.
Then I started overclocking my CPU, and right after my first BIOS change (all I did was changed clock speed to 4.6Ghz from the stock one, nothing else) So when I get to my desktop the lag starts and its huge, mouse has a 2 to 4 second delay and moves stuttering, programs open very slowly etc etc...

But after like 1min or 2min all works fine again. I did a BIOS update after this, no effect.

 

[derekullo]

It sounds like your cpu is throttling.

2 minutes of 4.6 gigahertz followed by 2 minutes of 1 gigahertz ... on a loop.

Is the issue fixed with stock cpu frequency?

 

[Kaluditz]

Yes, when BIOS is on default settings it works normally. What is causing this then? I'd like to keep the overclock as it gives much more gaming performance.
Also I have good cooling (NZXT Kraken X52, liquid) and doing some TimeSpy it gets max 75C. And my current OC was at 4.8Ghz with voltage set to auto.

 

[Kaluditz]

Ok I have no idea what the problem was, now after I booted up with stock BIOS settings and after that restarted and changed back to the same overclock setting (i have save/load slots in bios) I have no lag anymore at start up.