My drives are as follows:

Samsung M.2 (boot drive)

Corsair SSD

RAID Array  HDD

External USB 3.0 HDD

It is the Corsair hard drive that randomly disappears, sometimes mid-write even.  As you mentioned, a warm boot (restart) fails to fix the problem, but a cold boot (shut down, power back on) immediately fixes the problem, albeit only temporarily until the next disappearance.

I have tried replacing the SATA cable, changing the SATA port, updating my SSD firmware, and updating the motherboard bios (running 3.1 also), and the issue is still present.

My hunch is it's the motherboard as I've had this SSD on other motherboards, and it has performed nigh flawlessly.  All S.M.A.R.T. tests and hard drive health indicators come back green across the board.  My first guess would be motherboard issue, second guess would an OS or hard drive issue.

I don't know about you, but my motherboard has been a little finicky since day one.  First, there's the well-documented XMP Memory bug (http://forum.asrock.com/forum_posts.asp?TID=6860&PN=8&title=z370-extreme4-xmp-bug).  Second, I've had difficulty getting Fast Boot to work correctly (I just get a black screen on boot and have to reset the CMOS).  Now, hard drives randomly disappear.

Maybe it's wrong of me to blame the motherboard, but given how finicky it's been, that's my hunch.  I know Asrock typically has a pretty good reputation, but this motherboard seems like a lemon.  I would love to be wrong.  If anyone finds a solution, please share.

After some period of time that I have yet to determine, the Corsair SSD disappears from Windows 10. When I warm boot the system, I am unable to enter setup (just get a blinking cursor).

If I power cycle the system, I can get into setup, the Corsair drive is there and if I boot into Windows the drive is present.

I am running the latest 3.1 BIOS and this occurred on the previous version as well.

As I write this the Corsair SSD is present and working properly.

Any ideas?