It is not recognizing the Bookcases around it for the Bookcase discount. This problem appeared with the last pack update.

The discount system was redesigned in the last version of the mod.
It now requires a multiblock structure in order to get the discount again - The Shrine!
Here is the Official link to the mod's wiki where the dev explains how to get it fully working again!
https://github.com/frqnny/dark-enchanting/wiki/Dark-Shrine---How-to-get-Discounts-with-the-Dark-Enchanter