I suspect your RCM Loader is a real one since it lights up blue when connected to a powered USB. But you should check that
page just to make sure. Check especially on the second
picture, for the USB C plug. The real one has a jigsaw pattern on the back, whereas the fake one has smooth metal with no pattern. I have a real one here, and can confirm the presence of the jigsaw pattern. Anyway, real or fake, you have a jig, which came with your RCM Loader, so remove any tinfoil stuck in your joycon rail, and use the jig itself, much safer. On the subject of your serial number, are you absolutely positive your serial starts with XAJ00050 ? Cause it's not even listed on this
page, and it should be. Are you sure it doesn't start with XAJ1005 or something similar? Cause that would mean the Switch is patched and you've been chasing a wild goose all this time.
EDIT:
@pic1972 is right, maybe your motherboard has been changed. You should check the serial in the system settings of HOS, just to confirm the serial number.