another thing I discovered and should be carefully taken care of, is that if you change your C++ properties after you have created a derived blueprint, properties can be messed up with because the blueprint will serialize them and can mix things up when loading the BP and deserialize the BP parameters after your changes.
Typically sub components will be set to null, but I have also seen two components of the same type have their parameters exchanged ! The solution for this is to declare the property with the specifier SkipSerialization