Bug : "Crown of the Magister" achievement won't unlock

Yo,

Version: 1.2.15 - Public

Where?: Manacalon Ruin

How? : ////////////////////////////////////  

Who? : ///////////////////////////////////

When? : Classic game, same version as in my first playthrough.

I finished the game once and realized i didn't get the "Crown of the Magister" achievement which should be one of the easiest to unlock as it is story related. Thus, I decided to create a new game with new characters in order to get it. Still doesn't work even if i try with each character. I tried to come back to Caer Cyflen and trigger the next quest, still nothing.

I'm not using any mod. I'm playing on Steam.

Thanks for fixing this,

Joos (A guy who wants to get 100% achievements)