Whenever Siege Raids arrive, the blueprints are there but the raiders don't build them. Latest instance the artillery blueprints were for uranium and plasteel, which they don't have enough of.
Constructors have at least 6 construction skill. I even lowered the Building Def to 5 skill, doesn't make a difference.
Most of the time they are medieval raiders, but sometimes they are industrial and they still don't build. Are Medieval raids supposed to get catapults or ballistas?

Does anyone know a fix for this? Or generally where I could find the Def that allows these on raids. OR how I can force artillery to be steel (I thought this was the case already)?