Apple Books won’t play audiobooks

I can’t believe that this isn’t a known problem, but my Books app simply won’t play most of my audiobooks. This is a long-running problem that’s got progressively worse over the last year or so, and is unaffected by whether the audiobooks are downloaded or not. I’ve tried removing and re-downloading audiobooks, I’ve tried accessing them the audiobooks tab and via the ‘Account’ menu, and I’ve tried reinstalling the Books app and doing a phone reset. I’m a long time user of apple products so obviously it’s nothing obvious like ‘have I correctly purchased/downloaded the audiobook’. All of these audiobooks played at some point in the past - but now, when I click on them, the icon just enlarges slightly as it registers my finger press, but then does not play. Most of these audiobooks also display just grey rectangles rather than proper cover images in the menu, but this seems only weakly correlated with the problem - sometimes books with cover images don’t play, and sometimes those without them do.

Any fix for this? Really irritating and a basic breakdown in functionality. It’s only on my iPhone - the iPad version of books on my same account seems unaffected.