@rvxk9n: Ok.. now it's time to play Sherlock Holmes!!
1) You started through SKSE
2) Mod did not activate!!!
3) First hire was with the old system.
5)You came back later to play
6)Mod was activated
7) You hired another follower with the new system from UFO
First follower was stuck in old system and bugged
Confirm Please!! Load save before having UFO and hire for first time again!!
Also always load newly installed mods with original game launcher..
I am 100% sure this is your issue!
@mavarg: It will work on custom followers but they will not have my unique fixes like: Housecarl AI improved.. since they are not those followers
2) If modders gave them outfits, you will not be able to use fully tradable inventory BUT in an update this weekend, i think, i will add a dialog option to tell them to remove those outfits and work with the UFO gear system!