GA-AB350N-Gaming Wifi - Samsung 960 Evo M.2 NVMe at PCIe 3.0 X2 reduced speed

[origami]

For some reason, my GA-AB350N-Gaming Wifi MoBo with
Ryzen 7 1700 CPU running Windows 10 (UEFI) will only run
Samsung 960 Evo NVMe at PCIe 3.0 X2
which is half the supported bandwidth of X4. 

This is confirmed by Samsung Magician 5.1 as well as CrystalDiskInfo. 
I've installed all the latest drivers, firmware and BIOS and
I've tried different settings but just couldn't get it to run at full speed.
Unfortunately, I don't have another system to do an isolation test on the NVMe.

List of things I've tried:
- Disabling APU SATA controller in the BIOS
- Resetting the CMOS (leaving jumper overnight), with battery removed
- Removing the NVMe, cleaning the contact and replacing a few times
- Running the NVMe on it own, with the SATA Controller disabled in Device Mgmt
- Switching Power Option between High Performance and Ryzen Balanced
- Disabling XMP
- Disabling Fast Boot
- Re-installing Windows on the NVMe

Is anyone with this MoBo and Ryzen CPU running NVMe at PCIe 3.0 X4 full speed?
Thanks in advance.

[rodf]

Well I have an AB350M-Gaming3, Ryzen 1700 and 960 EVO 500GB and Crystal disk info reports it is running at PCIe 3.0 x 4.

Might not be relevant but in Samsung Magician it reports I am using the Samsung driver - could you be using a default Microsoft driver ?

[rodf]

Actually just remembered this from the manual:



Does your board have this and are you using those ports ?

[origami]

Might not be relevant but in Samsung Magician it reports I am using the Samsung driver - could you be using a default Microsoft driver ?

I have tried both the Samsung and Microsoft drivers but it did not make any  difference.