I’m putting this here as I believe it’s most likely a map that was missed when most were brightened up a bit, therefore I don’t see it as a bug.
Doing the monos for Ending the Storm (non-empowered), after the second quest echo the Echo of a World is very dark. This is in stark contrast to the other areas and the Echo of a World normally.
Dark Echo of a World
Edit: I did just open that picture and it really doesn’t do it justice just how dark the area is.