I just purchased a used EVGA 1080 TI GPU and am having fan issues. The left fan (nearest to the plug-in ports) is ramped up to 100% and the right fan isn't running at all. I ran DDU and reinstalled the latest NVIDIA drivers with no change. I even pulled the card apart and applied new thermal paste thinking maybe there was a hot spot. Didn't fix the issue. Then used MSI Afterburner to manually adjust the fan and no change. GPU-Z shows fan speed at 40% (where I set it in Afterburner) and Fan Speed RPM at 0, which isn't correct. Any help would be greatly appreciated.

The feedback wire from the fan could be bad, or the feedback circuit in the fan hub could be bad.  Otherwise, the fan controller on the card could be bad.
 
If you can't return the card for a refund, I would first try replacing the fans.  If that doesn't work, I guess you just have to hope to find an "easy" fix for a potentially broken fan header pin on the card, or simply live with it.