just because the memory works in a different board doesnt mean the memory wasnt at fault. glad it worked out though. don't buy ram separately in the future. you probably wasted a lot more time swapping the board.
I understand your point, and i think your recommendations is valid 99% of the time since its safer to buy kits, and the next time i surely follow your advice!, but this time it seems the prime x370 pro was faulty, and the main problem was that one slot was failing, and not only ignored the ram, but also affected the neighbor slot, so this time the issue was the board..
Anyway, thanks for your response!! i was really worried...because it was the first time i built a computer. But well at least i learned a lot of stuff