This seems to be an ongoing theme with ESO... I've found several quests bugged where a NPC follower is supposed to lead or follow and they either don't, or they follow but the interact option never appears. There is a quest in Greenshade where Indaenir is supposed to follow you... he doesn't... so when you reach the point when it says, "Speak to Indaenir" you actually have to log out and back in for the him AND the prompt to appear. It was noted years ago, fixed, then following update broke it, months later it was fixed again, only to be broken by another update. Now, they just don't seem to care and it's been bugged for years now.
I've notice companions will disappear if there's a npc attached to the quest. A perfect example is when Garyn follows/guides you to Holgunn (Davon's Watch - Delaying the Daggers). Your companion will track the same path as Garyn and then disappear when Garyn returns to his duties with his father.This seems to be an ongoing theme with ESO..
Perhaps they can fix this as part of their 'bug fix' list this fall.
logging in and out did not work for me and I had to abandon Isobel's intro quest 3xs on one toon before the stars aligned and I could finish it.