Arbiter of Ash skill books not dropping

I beat the Arbiter twice in normal and harder version and with normal and the red fragments, but it never dropped a skill book, and I am unable to skill "The way forward".

I used all skill points and my boss tree is maxed and Doyani also has no books.

Am I missing something, or is my character just bricked and I won't be able to progress due to a bug?

Read the patch notes, I am stupid.

What does the patch notes say about this? I can't find anything about it.