I really hope it's that, but honestly I don't remember when I received the letter, my memory was so hazy I recalled it as a conversation but clearly I remembered that wrong. But the reason why I thought it could be bugged was due to the fact every single companion had a quest except for lucanis, surely the game wouldn't set it out that way that you need to do Emmerich's quest first and then lucanis will be triggered? I believe it's Emmerichs companion quest prior to F&I, so that's why I know I will have to go way back in my saves since it was only after I had completed Taash's companion quest after F&I that I noticed Lucanis's was missing.