Windows won't boot with two graphics card installed

Here is my system info:

Windows 10 pro 64 - ver 1809 - build 17763.195


Asus Prime Z390-A motherboard

64GB (4x16) Ripjaws V series DDR4 2666 CL15

2 x ADATA XPG SX6000Pro 512GB PCIe Gen 3x4 M.2 2280 NVMe drives (RAID 1)

PNY Quadro P2000 graphics card (with latest BIOS updated from PNY)

PNY Quadro P400 graphics card

(All drives and BIOS are updated and current)

If I only have one card (either the P2000 or P400) installed in either the x16_1 or x16_2 slot, the system boots and runs fine. Once I add the second card, Windows will try to boot, pausing up on the spinning dots a few times, and then give me a blue screen stating I have no bootable drive. If I go back into the BIOS, my NVMe (RAID 1) drives are gone. But, if I shut down, remove one card and power the system back on without entering BIOS, everything boots fine. If I do enter the BIOS, my drives show and everything is back to normal.

Is this a GPU issue or a software issue?