Always ,before RMA ,make pictures to the hardware you send.
If you would have done that you would have seen the MAC address of the onboard LAN which is unique.
The magnifier glass may be useless if there is a hidden manufacturing issue.Those pins go tru a multistrat PCB so you wont know where it s not in contact ,properly soldered.
Changing the PSU will allow you to isolate a possible tired connector.This clips in the ATX connector can get loose over time.It could be that this board to have the pins with a smaller gauge for some reason so the contacts to be imperfect.
If it s a modular PSU it s even more prone to such on both ends.