I have reached Rank 20 with Undermine as an Alchemist/Engineer and was able to purchase the Engineering book, but the Alchemy book remains locked and says I need to be Rank 16 to purchase it.
Did you recently change to Alchemy?
having the same problem none of my old alchemists can buy the book but making a new alchemist allows me to none of the other professions are doing this to me I have about 8 alchemists who would like the book without dropping alchemy
I have been an Alchemist/Engineer for several expansions now, I have not recently changed. Good idea to check, definitely!