Low editor FPS on second monitor

I have two GeForce GTX 1070 video cards.

I have two monitors, each monitor is plugged into a separate video card.

Each monitor is 60hz refresh rate.

The PRIMARY monitor always runs UE4 at 120 FPS.

The SECONDARY monitor always runs UE4 at < 30 FPS.

Each monitor performs at 120 FPS when made primary.

This is even with a single UE4 window open.

I’m running Windows 10.

How can I get the 2nd monitor to run UE4 at 120 FPS like the primary monitor?

Yes, I DO have Geforce Experience In-Game Overlay turned off.