Download the licensee repro from here - [Link Removed]
There are three issues on display:
Shadows under the spheres are blurred:
Cubemap darks after certain distance when HDRI backdrop size >=3000:
Reflections and lighting lost when HDRI backdrop size <= 410:
See linked UDN for further information.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-174893 in the post.