M2 SSD not detected in slot1, but is detected on slot 2

[Hoffmann__]

mobo: Asus Rog Strix B550-I

SSD: Corsair MP600 NVMe PCIe gen4 x4 M.2 SSD

 

other parts:

AMD Ryzen 5900X

RTX 3080 Asus Tuf Gaming

Corsair Vengeance LPX 8gb (plan to replace this later)

Corsair SF750 power supply

 

 

when connected to slot m2_1 (front of the mobo) the SDD is not detected by BIOS or windows install

when connected to slot m2_2 (back of the mobo) the SDD IS detected by BIOS AND windows install, works fine

 

I don't have another nvme SSD to test slot1 (those darn things are pretty expensive), but the problem is definitely not the SSD as it works fine on slot 2

 

In this specific board the slot 1 uses pcie 4.0 lanes while the slot 2 uses pcie 3.0 lanes so I am wondering if there is some setting I need to enable on the bios. I tried several different settings on the bios (including changing pcie bifurcation mode to 8x 8x) to no change 

both devices are brand new. I tried updating the motherboard BIOS (from factory to 1801 x64 version) to no avail

 

Could use some help here, completely lost and I really don't want to get the mobo replaced and possibly run into the same problem again