I have a brand new Zbook 15 G3 that I have completed a bunch of upgrades on - full 64GB, 1 TB PCIE SSD, 512 GB PCIE SSD, 1 TB Micron SATA SSD. Both PCIes work fine, recognized by BIOS and the OS. The Micron SATA SSD however is recognized only by the BIOS, not by the OS - Device Manager, DiskPart or Disk Management, do not see it. I am booting from the 512GB PCIE SSD. I played with all the BIOS settings, but so far no luck. All the SSDs have been puchased through the HP site with HP part numbers as specified in the laptop specs.
The SATA SSD is fully functional, I am able to see it if I attach it to a SATA to USB connector. It is not recognized however when attached to the internal SATA cable. If the original HDD is attached to the internal SATA cable, it immediately appears in Disk Management or Device Manager, so no issues with either the cable or the SATA SSD.
There is talk on the board of prepping an SSD. I did initialize the SATA SSD using the USB method, and created a partition with MBR on it, but still not recognized by the OS when plugged on the internal SATA port. Yes, the SATA port is visible to the BIOS. It does not make any sense that a device specified by HP for this laptop would not work uninitialized and be recognized by the OS - Windows 10.