From reporting UDN:
"We had a weird issue with new components added in C++ not being instanced properly on non-direct Blueprint children.
It seems to happen if loading of the parent BP is deferred. It might be related to the code inside USE_CIRCULAR_DEPENDENCY_LOAD_DEFERRING not instancing components in case of deferred loading."
1.) Create a new (blank) C++ project
2.) Save the level and setup as startup level
3.) Add a new C++ class to the project based on ACharacter, (AMyCharacter)
4.) Add an ActorComponent (e.g. a capsule) to the character in C++ just for reference (this one will behave correctly)
5.) Start the engine, create a blueprint based on MyCharacter (BP_MyCharacterBase)
6.) Create a BP based on BP_MyCharacterBase (BP_MyCharacterChild)
7.) Open BP_MyCharacterBase, add a variable of type BP_MyCharacterChild to the BP (so the parent references the child)
8.) Place an instance of BP_MyCharacterBase on the (startup) level
9.) Save everything, close the editor
10.) Add a new capsule component to AMyCharacter in C++
11.) Start the engine
Observe the following:
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-132711 in the post.