There is a bug on material instances include refraction.
It occurs when original material is opaque and instanced material is overridden blend mode translucent.
It doesnt seem to show refraction for that situation.
Version 4.7.0 Preview 1
Hi caner_ozdemir,
Please make a post on the answerhub at http://answers.unrealengine.com so we can better assist you. If you can, please include reproduction steps in your answerhub post detailing what steps you took before discovering the bug. Thank you!