What on earth could this mean?:
Object SubstanceInstanceFactory /Game/Empires/Effects/Effects.Effects from source cluster Material /Game/Empires/Effects/M_BuildableTest.M_BuildableTest is referencing object SubstanceGraphInstance /Game/Empires/Effects/SimpleGradient_INST.SimpleGradient_INST (0x000001fbca8e3580) from cluster Material /Game/Empires/Effects/Explosion3/M_Explosion3.M_Explosion3 which is not referenced by the source cluster.