Appreciate your response hugely, thank you. I ran into this issue 3 or 4 times in a row on my older system and rolling back to earlier drivers seemed to snap MSFS out of this state. Then I updated to the newest drivers (at the time) and MSFS still stayed happy for a few sessions until it happened again.
It looks like an initialisation thing. To have it happen on two completely separate systems is a concern. The only common factors are; Xbox pass version of the sim, Oculus Rift S.
One other observation that persuades me it’s an initialisation thing was a post here from a user who would exit/enter VR mode a few times and sometimes enter/exit fullscreen/windowed a few times before the performance ‘clicked’.
Another observation was prop ASW flicker that I would get sometimes when I had the fps limited via OTT. The sim would be smooth and fluid at 30 fps ASW on but the prop flicker would be there sometimes when I launched the sim and not others - clear skies, various setting changes would not make it go away, only exiting and restarting the sim (sometimes a couple of times) would clear it up.
I have reinstalled the sim again, will roll back drivers and launch it, then update drivers and launch it. I’ll try VR mode both times.
I am genuinely convinced that there are folks on here suffering from this issue who have mitigated it using tweaks and limiting fps. It’s only because I have had the sim running beautifully in VR for the first few hours of installing it on my new system before hitting this problem again that I am so certain it’s a hard bug. For those first few flights I had no OTT or Oculus debug running at all, I didn’t need it. I was running 100% TAA with high clouds (in the Cessna) and was pushing the odd setting up during the flight. Whole thing was stunning with occasional stutters during taxi (I can live with that).