Lighting getting darker in viewport (on ceiling most) UE 5.5

[TrafalgarDlaw059]

Issue :
Sometimes in editor viewport lighting came whatever the lighting I did , sometimes it’s getting darker.
If i restart the project then it’s coming correct, not every time but most of the time . it is the same for in package build also.
used UE5.5

so far I tried some of the things that I thought it might be causing the issue , But unfortunately they are not the culprit .
which are :
Post process volumes
lights ( rect lights) & mega lights ( I’m using mega lights for this scene)
ray tracing
auto exposure

[TrafalgarDlaw059]

I found one fix for this issue couple of weeks ago…

First of all the reason behind this thing is a huge combined mesh in the level…
While viewing in the lumen overview that huge mesh showing in the reflection view like a blackhole an absolute dark colour and in the Lumen scene it is full pink .
so I separated that combined mesh and fixed the geometry .(it is like 540 separate meshes).

I don’t know this is the solution but it does works well for me