There are purchased items on the iPhone “Terminal” that are not present on your Mac. Do you want to transfer these items from this iPhone back to your Mac?

Every time I sync and backup my iPhone to my Mac I get the message:

"There are purchased items on the iPhone “XXXX” that are not present on your Mac. Do you want to transfer these items from this iPhone back to your Mac?"

I always say yes, and the message always re-appears when I sync again even though there are no new purchases.

Both macOs and iOS are the latest versions, fully updated.

Both devices are authorized for my purchased content, in Books, Music, etc.

All available purchased content is downloaded on both devices.

Where can I see the list of what these items are? How can I determine if and when they are being transferred or not? Where is the interface for managing these transfers?