I'm unsure if any of you guys have this same issue, but my Chii is pretty much doing the subject of this thread. She can gain VIP from other vendors, bit Xivus is the odd one out. Plus her armor never needs to be repaired since it never loses durability when fighting enemies.
If this keeps up, I won't be able get the titles for better DZ percentage rates nor experience 
Quick edit: Not sure if it's related but I only cleared her up to Junk Pool for the main story quests. Maybe I'm totally wrong and just have to play her further into the game lol
