I have also tried on Gigabyte Z170X Gaming 7 board with a new graphics card GTX 970.
Same problem, the SSD can only be found once after cold boot.
I am going to exchange for another new Intel 750 and see what happens since I have ruled out all other possibilities.
As was mentioned in the some of the threads you referenced, we would advise to review the advisory Booting with NVMe* PCI Express*, look for the closest match for your motherboards and apply the configuration.
Make sure you Download Intel® Solid-State Drive Data Center Family for NVMe Drivers, version 184.108.40.2067.
Verify that the PCIe slot you use for the Intel® SSD 750 is operating at PCIe Gen 3.0 x4, you may need to check with the Computer Manufacturer which is their recommended slot; since some slots may be disabled or operate at a different speed depending on the CPU model and the devices you have in the system.
t is worth to mention that some motherboards have specific PCIe slots to be used with NVMe drives.
You may need to go to the PC BIOS and set the PCIe slot to x4.
Also you might want to disable any fast boot techonologies in the BIOS.
Hey aznxfrost, did you end up finding a solution to your problem?
I'm having a simmilar problem where the mb detects the card only sporadically