Licensee has provided a BP workaround
Download the licensee repro here -
View the three materials in the content browser. From the licensee:
_This is just a basic translucent material working as expected.
_Same material as above but MF_EmptyFunction is added which is just an empty material function which passes through the material attributes.
Again same as previous material but with a "fix" to reset the refraction value after the material function.
The Minimal_Default map has three spheres added. I would expect refraction to work correctly on all of them but the sphere in the center is missing refraction completely.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-121355 in the post.