some additional info: Not sure if this was always happening and I missed it, or if this is new, but now if I open the editor on a map where the offending bluepint is not on and open the blueprint the log actually shows the same error. This will at least speed up the detection of the problem (as I do not have to wait for the cooking) and tells me there is a problem with or around the initialization of the child actors. But still: does anybody have an idea?