6 Gpu'z no but 5 Gpu'z yes? Problem with Asus prime z270-p

[gilfel]

When I am running 5 gpu'z on my rig everything is fine, but when I add another one to 6 total I got trouble. (How can I put a picture to this message?)

I am using Asus prime z270-p MB.
Simplemining OS
Gtx 1060 gigabytes

* I tried to switch between the gpuz' the risers' the slots and nothing help.

BIOS settings:
Fast boot - disabled
4G enabled
Gen2


Thanks from advanced,
Gil.