Greetings:
I have two Asus Z170 Pro Gaming motherboards. Neither of them will run more than 3 nvidia cards. I am trying to get 4 GTX1050ti’s running on one of them, but I can only get three cards to run, one on PCIex16 Slot one and Slot 3, the third card connected by a riser. If I put a card in SLot 2, it won’t get detected 
I’ve confirmed this behaviour on the second system, both of them being identical in every way.
Asus tech support tells me that Slot 2 only works if the cards are in SLI. Does anyone have any experience with this configuration and what I can do to get 4 cards running?
Thanks in advance!
EDIT: The BIOS is the latest revision available.