Rumbutter gave the two workarounds for this issue. If those didn't help, unfortunately, it sounds like you'll have to wait for a bug fix as there as is no way for you to solve this problem yourself. There are a lot of companion bugs with 4.0 that are being fixed but this takes time.
If you are a subscriber, you can contact Customer Service; they do help with stuck class quests and can manually update the mission for you but I'm not 100% sure what their policy on companions is. Try writing an in-game ticket, make sure to pick the Quest category, not the Bug Reports category, and include all the details: your character name, your server name, the name of the quest and explain that you cannot continue the class quest with Andronikos missing.