This is what I ended up with..
I flashed the old bios on these cards, and I also had to set the power limit to +30% to achieve 28Mh/s.. so these "replacement" cards draws significantly more energy.
Very odd. I don't get what did they change.

Hi Guys,

Here is a very strange problem.
I have a bunch of MSI RX470 ARMOR 4G cards, I bought them about a year ago, all came with samsung memory.
All works fine hashing 28+Mh/s on ETH+DCR. However fans started to die on couple of cards. So I sent them back to MSI.
Instead of replacing the fan they sent me an another card(serial number is not the same).
Also came with samsung memory, the first thing that I noticed is the different bios.
original one: 113-V34121-F1
replacement one: 113-V34121-X2

So I did the same 1750 strap change in this "X2 bios" as well, however these cards don't want to hash with more than 24Mh/s
I tried the 1500 timing too, no matter what I do, the maximum hashrate that I get is 24Mh/s.
I have 3 cards like this.

What is different on these cards?
Have you seen something like this before?
Any idea?

Thanks in advance,

What do you mean they changed the chipset?! Chipset is made by intel https://ark.intel.com/products/90590/Intel-H110-Chipset
It is a ~2 years old ancient. MOBO vendors usually doesn't re-engineer chipsets.

Is this based on the H1110 chipset? I assume.
Max # of PCI Express Lanes on this chipset is 6.
So what is the minimum CPU requirement to be able to use 13 cards? 

How do you fix the cards?
How do they stay in place? Im planning to buy a case like this but I have no idea how will the cards stay in there.