I just wanted to share something some might not now. When adding another card trying to run SLI and in Gen3, I always make sure to run both cards installed without the bridge and a clean fresh driver install, after that I reboot and and install the 2,3 or 4 way bridge whatever you have then I open Nvidia and select SLI, after that I open GPU-Z and check, click on the ? mark next to the values of the Bus Interface, run it in Full screen Render mode and on the bottom left corner it will show you what each card is running, for example NVidia GeForce GTX XXXX (xxxx Your Card) PCI-E 3.0 x 16 @ x8 3.0 for each card installed.

mine looks like this
NVidia GeForce GTX 1080: PCI-E 3.0 x 16 @ x8 3.0
NVidia GeForce GTX 1080: PCI-E 3.0 x 16 @ x8 3.0

If you have a single card it should look like this
NVidia GeForce GTX 1080: PCI-E 3.0 x 16 @ x16 3.0