Books imported my ripped audiobooks from iTunes (Music) and will not play certain tracks, although all tracks are present and in order when I look into the Library folder.

Books imported my ripped audiobooks from iTunes (Music) and will not play certain tracks, although all tracks are present and in order when I look into the Library folder.

I am on macOS 10.15.7.

This is what Books plays, even though all the tracks are present and in the correct order in the library:

~/Library/Containers/com.apple.BKAgentService/Data/Documents/iBooks/Books/Audiobooks/

I have tried copying the folder with all the tracks and reimporting to Books with the same result.

Does anyone have any ideas on how to correct this?

I appreciate any help on this topic.