arkantos91
If the same stick will fail in another PC too, then we can conclude it's one of the ram stick that got somehow damaged.... do you agree?

Yep. Don't think you need to check it in another pc though.

Sounds like a textbook case of a bad RAM stick. As soon as your system initiates anything memory hungry and uses that second stick, it craps the bed. I'd try to RMA with the manufacturer if they'd do a single stick swap, I know a lot demand the entire kit back though, leaving you without a working PC. :(

A little update: tried both sticks in my friend's computer. This guy has a B450 Asus board: the good stick worked as inteded, the bad stick didn't even make the computer post at startup!
 
Then I had the chance to try my ram in another friend's computer, this time a Gigabyte X470 board (like mine, even if not the same exact model) and the behavior was very similar to the one I have on my computer. The PC starts and gets to Windows with the faulty 8 GB stick but doing a memtest86 causes the pc to reboot. 
 
The only thing that still does not convince me is the fact the sometimes it takes a little bit longer for the memtest to fail... sometimes it fails very quickly, other times it takes a minute or so. The answer I gave to myself it's that probably there is some "sector" of the ram that is damaged, and when that is accessed, the freeze occurs.
 
I have to go through the RMA process now and really don't know how much time it will take.... so in the meantime I bought some 4000 MHz Kingston (HX440C19PB3K2_16). I know they won't ever go to that speed but they're B-die so they should be a little better at least.

Yeah it could with pwm and whatever that Controller (removed)/Loosing the rails. This unit no..oldddd schoollll…..gotta watch Leakk/ripple get bad and get in...still acceptable but I see some (removed) on a meter...but that DOES still like them older like units. I can't find any 420uf's but yeah Probably fire up with 390s..Looks good though..should be good for awhile longer idling at 12.16v
 
 
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batboy88
Yeah it could with pwm and whatever that Controller (removed)/Loosing the rails. This unit no..oldddd schoollll…..gotta watch Leakk/ripple get bad and get in...still acceptable but I see some (removed) on a meter...but that DOES still like them older like units. I can't find any 420uf's but yeah Probably fire up with 390s..Looks good though..should be good for awhile longer idling at 12.16v
 
 
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I barely understood anything you said, sorry

I got my new 4000 MHz and man the B-die does make a lot of difference from the M-die!
The old ones weren't able to keep over 3000 MHz without blue screens all the time even in Windows idling.... these ones with builtin XMP profile at 3600 MHz gave me no issues (excluding PUBG, but it's well known it's very sensitive to memory stability).
I rma'd the old ones. Thanks for your help guys
 

 
Good job.