Games like this tend to have bugs that I can't understand. I recently played through an identical mission a friend of mine was having problems completing. In his game, on a different PC, the game crashes every time he initiated the quest. In mine, it worked without a hitch.

There's so many differences between our savefiles and our system configurations that the bug could be a combinatorial explosion of things without access to source code.

This is super common in videogames. When some significant amount of people are experiencing bugs with a game and you're not, you should defer to the judgement of the ones who are having problems.