UPROPERY Object set to null by the engine during startup

Hi,

I mean the parent of the blueprint is a C++ class without the Component directly but has inherited from a base C++ class. There are no higher class to parent from. I can create a temporary parent one in blueprint to test.
Do all UPROPERY objects get set to defaults automatically after the constructor is called. If this is the case, am I correct in assuming that CreateDefaultSubObjects assingments in constructor will get overriden?
The UComponent has UCLASS(BlueprintType, DefaultToInstanced), is that responsible for default value(null) assignment?

Thank you