NVME not detected

[Belgian Waffles]

Hey guys! 

Long time LTT fan, first time posting on the forum. 
I just built a new pc and got stuck on a specific problem: 
 

1. I built my new pc outside of the case first and ran a first boot. All worked perfectly. 
2. I mounted everything into the case and booted up... and now one of my two NVME ssd's (the one in the main (M2_1) slot is no longer detected in BIOS. 
3. I tried reseating the nvme, but nothing changed.

Considering the above, I am mostly thinking something might be shorting the ssd, but my case came with preinstalled stand-offs and I didn't lose any screws while building, so I can't really see what could cause a short

Does anyone have any suggestions as to 

1. What the cause of the issue might be?
2. What the best way to test and resolve the problem would be?

Thanks in advance for your suggestions! 
PS: the specs: 

Case: Corsair 4000D airflow

Motherboard: Asus rog strix B650e-f

ssd: Samsung 990pro

Screenshot below was during the first test run with both ssd's still showing.

[jmilne810]

I have the exact same issue, but it would appear that nobody has a solution to the problem 

[Harmsway1283]

Have you tried disabling intel rapid storage technology?

[AlfaProto]

Quote

I built my new pc outside of the case first and ran a first boot. All worked perfectly.

I'm assuming you only have iGPU running.

 

Have you checked the manual to see if that M.2 is tied to anything?

 

Image of your installed SSD?