I have the same cards on a ASRock Z97X killer motherboard and had a similar problem. Setting the second and third PCI-E x16 slots in the BIOS from Auto to GEN 3 solved it for me.
is this the same issue with the asrock z97 extreme 4? but if i set gen 3 i can't use the riser x1 slot anyway, do i need gen 2? in my bios setting i cna only see pcie x1 and x5 to set auto or gen which is the right one?
I think the problem is when set to auto the board configures the slots for SLI and overclocking. Since you are only using a 1x riser in the 16x slot, it can't detect the card. The other issue is Z97 has limited PCI-E configuration options in the bios. Some boards have other settings like 4G decoding that you need to set for the PCI-E x16 slots to work with risers. You also need to set the x16 slots to GEN 2 or GEN 1 on some boards.