Hello ,
Thank you for posting your question in the community and I would need to take a look at the scene itself to see what is causing this problem. You can check to make sure there are no fog object placed, and that the smog is off in the weather effects settings.
It could also be a light that is placed with the Haze effect on.
Try turning off everything in the scene graph except for the walls and ceilings then starting turning on elements until you see the behavior change. If everything is turned off and you still the this fog then we would need to investigate further what would be causing this and would recommend you submit a bug here: https://twinmotionhelp.epicgames.com/s/case-community-page
Kind regards,
Vincent B.