the problem was coming from a light that was positioned behind the hair. i don’t know exactly what was wrong with it since i used the same light and the same settings. so i ended up removing that back light, but i still haven’t found the main cause of the issue.
also, i found this free plugin: [Groom Hair Cinematic Tool UE5]. it makes setting up cinematic lighting in ue5 easier by providing a shortcut to access many console variables. might also check out those guys on linkedin.
hope this helps!
@benj_rouzier_2MA @Knoopmas