Cannot place variable X in external scope Y

Development Pipeline & Plugins Editor Scripting
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I haven’t worked with Blueprints for the last couple of months so now I’m catching up with the new features. One apparent change is that I can’t reference anymore an inherited component (originally added in the parent class): dragging it to the even graph shows the “Cannot place variable X in external scope Y” message.
Why does this happen? Should I create getter/modifier functions in the parent for each component?

EDIT: Binary 4.7.2