This problem is getting more obvious while Roughness value is getting bigger, 1 get maxmum difference
If surface has Normalmap applyed, because of this problem, bumpness effect is weaker on Mobile
It's a very old problem， I don't know which version it started, at least more than one and half years old
one of UDN issue
Unzip the folder attached into Content folder of 4.26 engine and open the map inside.
Switch between Mobile/ES3.1 and PC/SM5, see the difference.
The reflection looks much darker on mobile preview vs pc
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-106218 in the post.