Taxonomy term archive default loop returns 1 record instead of 8

Your code should hook the CPT registration to init, though I don’t know if that is part of the issue.

Your code is relatively simple, and it works just fine for me when I test it.

Unless you’ve altered the main query, on the /books/accepting-yourself archive page the Loop you’ve posted should return:

1. The published posts
2. In your “book” CPT
3. In your “accepting-yourself” term
4. Limited to the number you’ve selected in “Settings -> Reading” under
   “Blog pages show at most”

It really sounds like item #4 is the problem. If you can verify that that is not it, then my next guess would be that something is already altering the main query and setting the posts_per_page argument to 1— probably a poorly written callback for the pre_get_posts hook.

As mentioned, I tested your code and I do not get any unexpected behavior. Without more information, that is all I’ve got. If you can edit more detail into the question I’ll see what else I can do.