Alright, I'm at my wits end here.
MacBook Pro (Retina, 13-inch, Late 2013)
Mojave 10.14.6
Boot ROM Version: 432.40.8.0.1
MacBookPro11,1
I have an original Apple 256gb ssd, and bought a SK Hynix P31 Gold 1TB + Sintech adapter to upgrade. I've followed the above steps, and go all the way to the P31 firmware update, but the drive shows as "Not Responding" in the Hynix firmware update tool.
I have Windows 10 To Go on a 64gb external ssd, with Boot Camp drivers installed. P31 drive is installed internally. Ran Windows updates as well.
The P31 shows up in Disk Management in Win10 with correct 1TB capacity, but is not assigned a drive letter.
Previously, I tried updating the P31 firmware with it in an external enclosure, but that gave the "Not Responding" in the update tool too.
I don't think the P31 is faulty, because I was able to install Big Sur on it, and boot from it externally. However, once I installed it internally, it gave a "not permitted" symbol on boot up. Assuming this is because of the ssd firmware not being up to date.
I was suspecting that the Sintech adapter could be faulty, but if the P31 shows in Win10 Disk Management, then the drive is being recognized and I assume that rules out faulty hardware. I've gone through many different google searches, and reseated the P31 and adapter many times now. Not sure what to try next.