Never heard of this glitch in the Skyrim, didn’t find anything explaining it, so i hope if it happens to anyone else you can read this guide for help.
What to Do
So, this is a glitch that happens very rarely, during the “Hard Answers” quest in the Thieves Guild storyline when you must speak to Calcelmo, the glitch is that you cannot even talk to him, at all.
But you can still pickpocket him. So, please first make sure you do not have the Shrowded Cowl mask on, which is the Dark Brotherhood item that conceals identity, you cannot speak to anyone with it on (for the most part).
If you are not wearing it, strip down naked, wait 24 hours, and then enter and leave the area (go through a door with a loading screen).
If that does not work then do this.
Walk up to Calcelmo, and open up the console using the tilde key “`“.
Type in “Player.placeatme 0001338E” this should spawn in a Calcelmo that you can talk to, but now you have two calcelmo’s, but he is nice, so no biggy.