I think it has to do with KLAX night lighning.
Any idea ? did someone experience same issue?
Nobody else reported it before. It's surely something in your video settings and even if you don't see it at other sceneries, doesn't mean much, because each scenery is different.
Something that *might* cause this, are the anti-aliasing settings. Try different settings and if they affect fps and, be sure you don't use "Transparency Antialiasing", this is also indicate in the KLAX manual.