I have a similar problem.
I built a new PC (mainboard: msi mortar b550 wifi, cpu: ryzen 7 3700x, SSD: Samsung Evo 970 Plus).
At first I installed Windows 10 and everything worked fine. During the Windows install, I only used half the space of the SSD.
Later I installed Manjaro on the second half of the SSD. Since then I observe the following behaviour.
The mainboard frequently does not recognize the SSD upon booting. This mainly occurs upon reebooting. It is usually fine, during a cold start.
At first the uefi boot entry for manjaro was shown. However, after some time it dissappears in the bios. I then reinstalled manjaro, but observed the same behaviour again. I’m not sure, if it is the bios, that reverts something after several unseccussful boots when it can’t find the ssd.
What I find difficult to understand: should the detection of the SSD not purely be hardware related? How can the installation of an OS affect it?
And of course I am wondering, how I can get to a working installation of manjaro.