Dell T3420 sometimes cannot detect M.2 NVMe SSD

Dear All,

I am not an expert in IT. My Dell Precision T3420 SFF has the latest BIOS 2.18.1. Recently I installed WD Green SN350 240GB M.2 2280 NVMe SSD. My pc also has another one SATA drive (D). The M.2 has the OS Windows 10 Pro. Everything is updated. 

The issue is the PC sometime does not boot, says NO boot device found, but sometimes boots nicely. I have removed the SATA and tried, but still the same issue. I have played with the BIOS, which is always been Legacy, but nothing helps. When the pc does not boot, the M.2 is NOT detected in the BIOS. 

Only one solution I found is that if I remove the M.2 and reinstall it, the PC will boot nicely. However, after couple of shutdown/restart the issue comes back.

Does T3420 meet the required criteria for NVMe SSD or it can have only the normal SSD?

Thank you. Any help will be really appreciated.