If you remove a post process volume from a level, it still doesn’t fully disable the post process effect. You need to go into the Project Settings → Rendering and disable features in there. These are the default settings that runs on the project. A post process volume replaces these settings however.
I think you can enable or disable the emissive materials in lumen, so that they will act like light sources.
The first thing I would do is to set the exposure of the post process volume to a static value to see if that helps.