Issue occurs because there is a legacy code path that forces all interface parameters to be declared as 'const' in function declarations, even if CPF_ConstParm is not set in exported C++ code. This case conflicts with our unsupported 'const ref' term type in Blueprint functions, and is handled for native C++ APIs that are overridden, but not for non-native Blueprint functions, which is how it manifests here.
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There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-93638 in the post.