Dmitry,
soccer_dan is correct in his statement.
The G1 series requires AHCI support in the M2 storage slot.
The G2 series can work with both AHCI or NVMe.
The supported M2 SSD in the 800 G1 is the 757990-001 HP part number. This is equivalent of the Samsung mz-hpu128t/0h1, also known as the XP941 - A 4 x PCIe v2.0 AHCI device.
In the next generation of Samsung M2 SSD using NVMe, the OEM SM951, which is the same chiset found in your 950 Pro, Samsung enabled both loads of the firmware in the same controller chip; AHCI and NVMe. THis new line is an evolution of their product line and firmware loads appear compatible.
This is why the Samsung branded devices work. They essentially use the same firmware family in two generations of product and appear to be compatible.
