Problem: I found the first three books in the Lachdanan series and then left the game. When I replayed it, none of the books dropped: neither the ones I found or the new ones.

Likely cause of the error: The lecterns are programmed to drop the first available book after the first book is triggered during THAT game, but without repeats. If you replay, you never get the first triggering book so the game never advances the book count. I.E. it is a series of boolean switches rather than independent switches.

Oddly, Leah's books will respawn in any order, but I assume that is because they are event triggered and not chronology triggered.