iOS 18 - Audible content not playing in Books app

Hi guys,

I use Books on MacOS to manage my audiobook library - there's content in there from various sources including Apple Book Store purchases, ripped CDs, files built via an Audiobook Builder app and content downloaded from Audible imported into Books.

Since moving to iOS 18 and Sequoia content purchased from Audible then imported into Books on MacOS plays just fine, but if I sync that same content to Books on my iPhone it doesn't play (it used to play before I moved to Sequoia and iOS 18)

Notes:

• I've tried de-authorising AND re-authorising Audible on MacOS
• All other content synced to the iPhone plays just fine, only content imported to Books from Audible fails to play.
• My workaround is obviously to listen to Audible content via the Audible app, then when finished mark them as completed in Books on MacOS but I'd prefer to do everything in the Books apps.

Has anyone else had a similar issue? If so have you found a solution?