I'm seeing the same behavior as Mark (at least I assume this is what he's seeing). Similar situation - the latest P3D and video drivers, a more than capable PC, and Prepar3D runs very smoothly normally (full screen, 4k). While using FlyInside, the display on the monitor is quite smooth, just not in the headset.
One other thing worth noting is that I've used FlyInside with the DK2, and it ran fine. That was a previous install/version of P3D though, so maybe not a good data point.
Here's a video I took of what I'm seeing through the CV1: https://vimeo.com/172059519/807419206a
As you can see, extremely jittery while I'm moving my head. If I keep perfectly still, the shaking subsides.
I did have a few add-ons installed, but I've disabled everything.