i got the asus Z270-P and 13GPU's

i have problems getting more than 7 to work.
I got this pcie extensions. Looks like a riser but u can connect up to 4 risers to it.
When i connect 8 cards. Sometimes it only get 5, sometimes 6 and sometimes 7. But never all the 8.
Also the system keeps crushing, and flashing black screen.

Is it at all possible to get more than 8gpu's working on that board? I have problems getting the riser extensions to work ~~

i am using windows 10, but rdy to change the os if this will solve my problem ~~