As the title states, the Akashic Tome seems to be refusing to accept new books.

I tried regenerating the Akashic Tome config on both Server and Client, and then attempted adding the Immersive Engineering Manual, which is specifically whitelisted, to the book; no dice.

There was a world reset on the server recently, with the caveat that the playerdata files were kept, thus allowing people to "pack up" and move all of their stuff to the new world. There was a pretty major update to the mod-list during this time. Prior to moving to the new world, the Akashic Tome worked just fine.

As I said, it's refusing to accept new books. Any book that was already in the Tome from the last world stayed there, and the Tome can still be used to access and switch between those books. The only thing that broke is adding new books to the Tome.

Can having too many mods cause this issue, maybe?

Found the issue, it was with a different mod. Should've expected as much really.