If an instance of a child BP has a non-default value for its parameters, that value will be ignored in the cooking process if the parent BP is nativized but the child is not and the default value from the child BP will be used instead.
Regression?: No
This occurred in 4.18 and 4.19
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-62338 in the post.