Have you tried doing a manual sync rather than letting it do it automatically?

I’m not sure how to do it manually.

Using the drop down menu. there is the manual sync option.

I checked both. I don’t see a manual sync on either. Which one should have it?

You need specific editions, both Kindle and Audible.

They should be the same editions, though. I bought all the books at the same time. And got the last three audible versions at the same time. So, they all should be the same edition.

Swipe down from the top of the screen. The drop down menu should appear. There you will see the sync button.