I think I’ve finally figured out what went wrong.
Before carrying out this task,
I had summoned a large number of items and study books from the console,
and used a huge amount of learning points in a very short period of time.
That seems to have triggered a series of bugs I hadn’t encountered before.
1 reply
This was caused by Levelsystem, a huge monolithic all-purpose quest. If it became overloaded or overridden by an outdated mod, it would bring the whole game to its knees. This is why it was dismantled into smaller independent components in 2.1+.