PostEngineInit just means the Engine has been initialized, but not that a world has actually been created.
You can see a list of the various phases and their descriptions here.
It’s difficult to give you direction as I don’t know the requirements for your call. If you just need a valid world, you could look into hooking into something like OnPostWorldInitialization. But if you need to make that call every time someone adds/removes a Static Actor, then maybe doing it in a background or finding some hook for when an object is added to the world (I’m sure there is one - I just can’t remember one off the top of my head) would be better.