Can confirm this. The UText3DComponent class is not decorated with Blueprintable or BlueprintSpawnableComponent in C++ (as it should be?). Since it is also marked final, there is no way to create a blueprintable sub-class (except overwriting the source file).
This is especially a problem, because a nested Text3DActor inside another Class (using ChildActorComponents) will break and become visually bugged in 50% of the construction script reruns. Might post another bug report on this one tho.