I tested each card and riser in their proposed slot individually.  Each ran by itself for 1 hour without any failures.  So kind of ruling out any hardware failure type issues.

All 3 cards are in the system, and load up quickly and available.  I am getting video from 1070ti in the primary x16 PCIe slot

The system now locks up when mining around the 5-6 min mark.  I tried the VertCoin miner real quick, and while it ran a bit longer the system froze eventually as well.