Some ePubs or PDFs are on your device, but do not appear in iMazing.
You are probably using iCloud to synchronise the contents of the Books app. Unfortunately, documents and eBooks synced via iCloud are not available to iMazing until they are downloaded in the Books app.
To download your books from iCloud:
- Launch the Books app on your device
- Go to the Library tab
- Tap the book of your choice which is not appearing in iMazing (you should see a small cloud icon on it), this will download the book on your device
- Click the Refresh button in iMazing