So, the darker one is the correct lighting, and it exclusively displays correctly after saving. That’s bizarre, and I’ve never heard of it before in the forums or AnswerHub, and I’ve read lots of posts. It sounds as though in the code somewhere, it renders the lighting upon saving…though it should be doing it during the change. Is the scene completely static lighting? or are there stationary and/or movable lights? Is there RT?
The lighter one could be the auto exposure settings. There’s also atmospheric fog and exponential height fog settings that can do it too, such as strong scattering and high density values. The other possible cause, which it could be in combination with the other(s) I referenced, is certain AO settings are incorrect to produce what’s in the second photo.