Incomplete audiobook in the Book store

I recently purchased and downloaded an audio book from the Book Store. It is the 6th of a 7 book series and have enjoyed the recordings to date.

However, this audiobook stops half way through the story at 6h33m (even mid sentence, not a break in chapter etc). The audio book in question is: "Promise of Wrath: Hellequin Chronicles, Book 6 (Unabridged)" by Steve McHuge (Narrated by Simon Mattacks).

I have asked others with Apple devices to check their Book Stores, and the store returns the same data: 6h33m and 303.4mb in size. This is (roughly) half its counterparts length and size.

Can iTunes or by extension, Brilliance Audio (Publisher), provide support / reason for this? Remediation would greatly appreciated.

Has anyone else in the community experienced this with other titles? If so, were you able to resolve and by what means?

Thank you in advance.