The BindWidget meta specifier allows us to bind a native widget pointer to a widget added to the hierarchy of a UserWidget in the widget editor. However, it appears to only search for a matching widget in the class that directly inherits the native widget class. Descendants of that class will throw compiler errors, despite the fact that they should inherit the widget and be able to manage the binding correctly.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-54061 in the post.