MSI B250M Mortar + ASUS GTX1070 STRIX

Hello, fellow miners! Here is my setup:

  1. Motherboard MSI B250M Mortar (https://www.msi.com/Motherboard/B250M-MORTAR.html#productSpecification-section)
  2. 3 x ASUS GTX 1070 STRIX
  3. 3 x ver. 6 powered USB risers (Molex with SATA/Molex powering)
  4. 1 x Corsair VS350 350W (for motherboard)
  5. 2 x Corsair VS550 550W (for every 2 cards 1 VS550 PSU)
  6. G3990 Intel processor

If I install my video cards via risers, the hash rate is terribly low and the third card is detected with error 43 in Windows 10 device manager (also the oprating system is unstable - booting up too long, sometimes not launching the networking, sometimes resulting into the screen of death). If I put 2 cards directly into PCIe 16x slot on the motherboard, they work great with proper hash rate.

Below there are some versions of what is going on and what I have done to tests it:

1. Bad risers
No, all risers were tested on another motherboard and they worked great.

2. Cards or PSU's are corrupted
No, when cards are plugged right into the motherboard, they work as they should

3. Motherboard settings
I've tried altering all the available settings for the PCIe on the motherboard, no good

So, the most obvious reason is that the motherboard does not support raiser cables - is it possible? Today I will get another cables, but the ones that I have right now work great on another installation.