Maximus XII Apex - Only 2 of 3 m.2 NVMe drives showing in BIOS

[fadingsignal]

Hello! I just finished a new PC build and am only seeing 2 of the 3 m.2 NVMe drives I installed showing in the BIOS. One of them is in the main motherboard slot, and the other 2 are connected using the DIMM.2 expander card.

I have a GeForce RTX 2080 Ti in the PCI 16x slot. Otherwise, nothing else.

How can I troubleshoot this?

Two of the drives are Samsung 980, another is a Samsung 970.

The full specification of the build is here: https://pcpartpicker.com/list/C6ghp2

Thank you!

[fadingsignal]

I replaced the ATX 24-pin and the three 8-pin power cables for the video card with custom ones from CableMod.com and suddenly the third drive showed up. What the?? Seems like maybe there was a power issue happening somewhere. Mysterious.