Hi
I am having sort of the same problem, but not with 1 or 2 companions, but rather all pf them as far as I can tell.
The promt to "I need to speak with you" and text bouble with pop up, but as soon as you clikc it, it goes strait to default dialog and doesn't progress. It has so far happed alot with Aloth, Edér and Tekéhu, but his is the most broken,
At the end I rushed the game to the end, and found out it is rather broken, as after you fight the guardian and enter the next zone, all the companions got conversations promts, yet none of them worked and poor Tekéhu lost even his default dialog (as it wont open at all).
Funny part is that the companions quest them selvs seam to get completed, yet still no new dialog.