Question ASRock X470D4U M2_1 Not Detected

May 15, 2021
I recently built a personal server for a homelab with the following:

ASRock Rack X470D4U
AMD Ryzen 5 3600
64GB Crucial Ballisitx 3200Mhz DDR4 (CL16) (Runs at 2666Mhz)
x2 WD Blue 3D NAND 500GB SSD - SATA3
x2 WD Blue SN550 500GB NVMe PCIe SSD
BMC: 2.20.00
BIOS: L4.21

While near everything worked from the first boot, I am having issue with the M2_1 slot consistently stating "Not Detected" in the BIOS or accessible within the OS (Proxmox). M2_2 supports either PCIe Gen3 x2 or SATA3 and I have tested the drive(s) in this slot confirming they are not dead. M2_1 supports PCIe Gen2 x4 which I have reached out to WD to confirm the drive is backwards compatible from Gen3 to Gen2. I have incrementally updated the BIOS from the shipped version to the current beta with no luck. However, every so often during a reboot the drive will appear and be accessible both in the BIOS and the OS. Until the next boot.

Is there potentially a BIOS setting I am overlooking?