When I get only 25fps, without using any motion smoothing trickery (which I personally find worse than what it tries to mitigate, anyway), on an HMD running at 75Hz, that means each frame is displayed three times.
My brain, however, has none the less detected an optical flow in its view, that indicates motion, so it
expects things to move steadily between every frame, and when they don't, but stay behind at their old locations, I get a ghost image of the things back there, updating stop-motion-like, blended with where the brain knows they
should be; This all happens in my head, so it won't show up in any screen shots. I do not see it on a monitor, because the monitor is "just" an animated picture in my environment - it does not track my head movement, nor fill my view.
The reason this does not happen when while stationary in-game, but while turning my head, is that although motion smoothing may be off, the VR runtime still applies rotational compensation for one's head turning -- it pans the view to match the orientation of the VR headset in-real-life. This can not deal with translation, however, so if I
move around, rather than just turning, I still get the stuttering motion from insufficient frame rate.
The one-eye-bright-other-dark issue is a persistent complaint -- vote at the bugtracker, at:
https://issues.frontierstore.net/issue-detail/47312
Forum member Arioch keeps a record of VR-specific bug reports, at:
https://forums.frontier.co.uk/threads/odyssey-vr-specific-bug-reports-please-contribute.575557/
Even with "small" FOV mode, the Pimax 8k/5k shows more than every other common headset, at 120 degrees total (both eyes together), which is ten more than my Valve Index, and since the lens is so wide, you still see as far to the right when turning your eyeball to look to the right, instead of having the limits of the aperture occluding the periphery (EDIT: ...because your pupil moves closer to the edge).
The 140°, and 160° "normal" and "large" FOV options are most certainly welcome, but they do come at an accelerating performance cost. :7