I have the same problem.
Briarheart appears naked when I played a new game using only USSEP.
After checking the naked Briarheart, disable USSEP and go to the same place, Briarheart will appear properly in the appearance of Brierheart.
And if you also enable USSEP and go to the same place Briarheart is back to naked again.
Even with USSEP enabled, the followers of Briarheart, added with other mods, are looking properly in Briarheart.
Considering these things, I think that USSEP is the reason why Briarheart appears naked.
Sorry to trouble you, but I'm happy if you can check it again.