11gpu rig sometimes boots with less gpu

I have a Asrock H110 PRO BTC+ along with 11gpu (8x580 + 3x1070) and 3 750w psu. I had a problem with my first mobo that ended up just recognizing 6gpu (black slots, no white slots recognizing), so I got a new mobo and it works way better.

Even so, sometimes when the rig reboots it recognizes only 10gpu. A single reboot usually solves this problem and boots up again with 11gpu.

But I’m wondering what causes this… Maybe a config on the bios I’ve not made? Any clues?