audiobook chapters missing in books app on iphone

Hi *,

recently I've added a new audiobook (m4b file) to the Books App, which I've created with Audiobook Builder. Within the Books App on Catalina, chapter marks are shown correctly, but on iPhone Books App it shows as one chapter.

For older Books, which I've synced using Mojave, all works fine.

I've tried to re-sync all Audiobooks and things got worse. Now all the Books have no Chapters anymore.

Does anyone have an idea how to solve?

Thanks

Frank