I have Gigabyte GA-970A-DS3P mobo which has 
3 x PCIex1 slots, 1
1 x PCIex16 slot, 
1 x PCIex4 slot, 
1 x PCI1 slot and 
1 x PCI2 slot. 
Product Image - 
https://www.amazon.com/dp/B00CX4MUCC.
PCIex1 riser plugged in PCIex1_1 - works
GTX 1060 plugged in PCIex16 - works
GTX 1060 plugged in PCIex4 - works
risers plugged in on PCIex1_2 and PCIex1_3 are not getting detected.
Somewhere I read that if I use PCIex4 then PCIex1_2 and PCIex1_3 will get disabled. Assuming that is true, I removed GTX 1060 from PCIex4 slot and I see still those 2 slot do not get detected..
Am I missing anything here.
I also read somewhere that if I plug PCIex1 riser in PCIex4 slot I should be able to use PCIex1_2 and PCIex1_3 but even that is not what is happening...
Please advice..
Udpate:
Somewhere = 
https://forum.giga-byte.co.uk/index.php?topic=6994.0