Have you spoken to the guy on Korriban (Ziagrom ??) that tells you about the special items merchant in the Korriban cantina?
The Juhani sidequest is incredibly buggy, and the Special Items Merchant sidequest is known to interact with it, making both unstable or broken.
My suggestion re: Juhani and Xor - do not talk to Juhani all that much until after the Leviathan and visiting Korriban afterward. You can talk to her some, but do not advance far in her dialog or you will break the Merchant quest.
After getting the special items available, then talk to Juhani all you want, and bring her off of the EH to talk to her... Xor will trigger on Manaan, and also Korriban, and maybe Tatooine. You will meet with him once, then he will come back for the final confrontation on another planet.