Unfortunately, I had to RMA the motherboard. It happens that the NMVe connector was somehow faulty since the beginning. I don’t know if it’s a mechanical, electronic or logical problem, but this was the reason I thought Netac SSD had issues (and I changed it for no reason).
Unfortunately, hardware issues are the hardest to find. There's no decent diagnostics software that covers all of the various brands of Motherboards and peripherals, and rarely will OEM software diagnose a specific fault. Assuming the power supply is up to spec (at least the outputs can measured), hardware "guess work" often begins with Motherboard isolation and burn-in software, then adding memory sticks and peripherals one by one. Most of it is off-line and time intensive.
The above is why, when building a new box, it's best to start with good quality Motherboard from an OEM with a good reputation. (Supermicro, Intel, MSi, ASUS, Gigabyte, etc.) Similarly, a good quality power supply is not wasted money.