Gamma setting / lighting is unstable? (VR)

My usual gamma setting for VR for the previous stable version was 1.6. For the current OB I have to set it to 1.4

That would be fine, however it looks like the brightness is not stable, it fluctuates between mission restarts. When I launch the game for the first time, it's too bright, so I have to bring the gamma down to like 1.1 or even 1. But then with the subsequent mission restarts the game gets darker, until after 2 or 3 restarts settling back to being comfortable at 1.4

Same mission, same time of day, weather etc., obviously