Specular Doesn't Affect a Material with the Eye Shader If r.IrisNormal is enabled.
Found in 4.22 CL# 7053642, 4.23 CL# 8115738, 4.24 CL# 8302014
The specularity for both doesn't change at all unless you go to the defaultengine.ini for the project and change it to 0
The specularity would function as expected
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-79460 in the post.