Hi guys,
I just got the rig assembled and when i plug all 6 GPU, only 5 are showing. It's not a GPU hardware problem since i tested them all one by one on the mobo.
hardware :
mobo : Asrock H61 pro BTC
PS : 1000W
CPU Celeron G470
4 Gigs Ram
GPU : Gigabyte GeForce GTX 1060 WINDFORCE OC 6G
USB powered risers
I read that it can be a 4G decoding on mobo problem but 4G is not available in bios. Bios is 1.2 version. Last one is 1.4, i tried to upgrade it by using the 1.4 version on a usb stick but mobo does not find the stick. (i booted OS on it so format should be ok). I tried flashing using internet but i'm not connected due to the fact that i'm using a wifi stick.
I also read somewhere it can be a driver issue but i can't find it back.

In a few words, i need help.
Try swapping the riser with a new one. Most of the times, risers are the culprit for this kind of problems.