Unofficial Skyrim Special Edition Patch

The dark face bug happens when a mod modifies a npc face geometry and isn't provided with the resulting modified facegen data (mesh + textures). USSEP only adds death items and missing actor effects to Sybille, and doesn't affect the face geometry or tint. So, USSEP cannot cause this issue... You have another faulty/conflicting mod in your load order affecting Sybille (or perhaps vampires in general), as PS4 cannot carry the new facegen data due to Sony external assets restrictions. The last Bethesda "official" face modification for Sybille was carried by Dawnguard. Maybe you have a pre-Dawnguard mod affecting her, and that was badly ported?

Just a side note: you should point if the other bugs you are reporting are on PS4 or another platform. As previously said, Sony restrictions regarding external assets makes bug fixing almost entirely impossible on PS4... I feel bad to say it, but on PS4 the USSEP is a band-aid applied on a wooden leg...

I disabled all other mods except ussep but the problem persists, After I disabled USSEP though, her face is fixed.

I am having the same issue. I tried disabling all mods except the patch, but it still persisted. Once I disabled the patch the problem went away.

I'm not at all sure why this was the case, but Sybille Stentor did not have the correct facegen data forwarded into her edited record that Dawnguard changed.