'Decal Blend Mode' in the Result node is missing. The user that reported this noticed it when converting from early access to Preview 1. Their emissive decals stopped blending.
Decal Blend Mode will be greyed out in the Material section.
Decal Blend Mode is missing.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-145209 in the post.