I've done just about everything I can think of at this point. I just replaced the Riser with a brand new one and still nothing.
All 5 of my other cards are working fine, but the 6th wont show up anywhere.
I've checked and refreshed the device manager.

MSI Pro Solution Intel Z170A LGA 1151 DDR4 USB 3.1 ATX Motherboard (Z170A SLI Plus) is my MB.

I really need to get this 6th GPU running and would greatly appreciate any troubleshooting advice.