I've been trying to register on this forum for about 4 months, so this will be an updated post.
In March 2020 I've bought a WD HC310 (0B35948 HUS726T4TALN6L4) HDD, connected it to GA-Z97X-UD3H, booted the system once OK, initialized the HDD in GPT, rebooted and it froze during POST.
I've started a few posts on different forums and also opened a ticket on ESupport. Told them everything, every detail, suggested my help in any way possible, even sending them a similar HDD, but they kept telling me they are testing something. They've sent 3 different BIOS images, which didn't fix the issue. In the end they told me the model of the HDD they tested with - not a 4Kn drive! And now they told me that they ordered a 4Kn drive "from abroad" and I have to wait another month!
With the help of other users of other forums, I found out steps to resolve the issue:
1. Enable the "Intel Rapid Start Technology" and set "Rapid Start store search type" to "PCIE AHCI/NVME Controller".
2. Save and reboot.
3. Disable the "Intel Rapid Start Technology".
4. System boots OK.
I have more questions, for which the support doesn't give a reply yet:
1. Why is the "Rapid Start store search type" option is read from settings, when "Intel Rapid Start Technology" is Disabled?
2. How do I mod the BIOS to have the "Rapid Start store search type" set to "PCIE AHCI/NVME Controller" by default, so if there will be BIOS reset, I won't have to disconnect the HDD to set the right setting?
P.S. I have a lot more questions, a lot of "hows" and "whys" about Gigabyte support, but I'm so fed up with waiting, so I don't really care about support now.