Hi,
Just sent you a skype msg 
I recreated a simple example case, and its still not working 
If I call the building function of the child from within the parents constructorā¦ nothing happens.
Here is an overview:
This is a simple BP that creates some meshes, based on an Instance and height offset parameter.
The implementation happens in the BuildStuff function.
This is the BuildStuff function:
If I place them in the level, they work like a charm, even at construction time:
So, now I define a struct for some data for the āMasterā BP:
And the Master BP also implements its stuff in a dedicated function, called BuildBPs:
The implementation of BuildBPs spawns now the SubBPs and calls its BuildStuff functionā¦
But in the editor, nothing is happening. Not at designtime, nor during gameplay of courseā¦
BUT: If I hook up the BuildBPs function in the master BP begin play event, like so:
Then I get the spawning during gameplay:
But this is not really usefull for a lot of reasons. I cant design a whole urban environment āinto the blindā and only see during PIE where my buildings areā¦
Since they are not spawned before BeginPlay, they cannot receive any lightmass attention. Hence the warning in the screenshot aboveā¦
Plus a lot of warnings about it:
Of course. I set them to be static, but spawning at Begin Play just isntā¦
So even with the function being explicitly calledā¦ Nothing happens.
If that would be fixed/possible, Blueprint would be a fully fledged āPrefabā systemā¦
Or am I still doing something stupendously wrong here 
Cheers,
Klaus