What could cause 'DuplicateStaticObject' stalling the launch?

I can’t really understand what is causing this. I tested packaging my project. Fiddled with some of the settings, tried to optimize stuff. I must have ticked or unticked a wrong box at project settings, or something?
Now every time I launch the game, it hangs for awhile. Once it starts up, it functions like supposed to.

Profiler tells me the cause is StaticDuplicateObject? But why? It didn’t happen before with almost identical setup.
My level is composed of little more than landscape, a little lighting, post processing and nav-mesh volume at startup when this happens.

What could be the cause of this?