Forward Shading under 4.25.3 seems to break something in the Hair shading model. Default Lit seems to behave normally.
Reported and tested in 4.25.3(CL 13942748).
Result: Shading is very flat with no specular highlight response.
Expected: Expect it to look very similar to the original under Deferred Shading. So you would see clear bands of specular reflections tracing the edge of the hair as you move the camera.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-98205 in the post.