WD SN550 1TB - low random 4K performance

Hi, I would like to ask you for help with solving of the problem I have with SN550 1TB, model number WDC WDS100T2B0C-00PXH0, firmware 211210WD.
From some reason, I have half 4K write speeds comparing write speeds I can see in reviews, for example on Guru3D.com.
I´m attaching my results in Crystal Disk Mark and also the screenshot from Guru3D.com
Same bad results are in ATTO.

At first, I thought I bought the defective piece so I bought another one to check.
Same speed results with the second one so I think there must be something wrong with my PC setup and not with SSD itself.

PC configuration:
AMD RYZEN 1600 @3,7GHz on all cores
16GB RAM ADATA XPG 3000 (2x8GB)
1x SATA SSD SAMSUNG 840 EVO 120 GB (system only)
Windows 10

All drivers, including AMD chipset driver are up to date.
WD Dashboard and firmware up to date.
Windows 10 up to date.

Any idea what might cause this problem?
I will be grateful for every advice.

My results:
DiskMark7_my test

Guru3d review results:
DiskMark7_guru3d review

SSDs slow down a little when the NAND is dirty (not all zeros). Furthermore, the IO intensive tasks on crystal disk mark are single threaded, thus if you hit a CPU usage via the application of above 8%, you will likely encounter a CPU bottleneck.

Maybe you are right. I can see that during the test, CPU usage is 8-10%.
Anyway I did the test in Windows Safe Mode and I can see much more better results:

DiskMark7_my test_safe mode

Therefore I think some active process is slowing down CPU/SSD.
I will try to do clear installation of Windows to see if results will be better.