Fixed layout epub does not work in Books

We have an 830-page InDesign file with images on every page and some 3,500 internal hyperlinks and maybe 500 external links.

If saved as a interactive PDF ebook it works exceptionally well. All the links work.

If saved as a fixed layout epub, the links don't work (though I should say that after one conversion from indd to epub, some of the links worked, but then stopped. Seemed strange to me :).

Each time I do a conversion to epub, a text box appears to tell me of errors in the file. These are them: 

• Unresolved Hyperlinks : 2 Health Bay-wD2 Seabreeze Cove-wD1
• External Text Anchor not found: 7
• Text Anchor in "/Users/jimmyb/Documents/a-Adobe CC/2026/A-PAGES/25-gulf-250306.indd" is missing: 1
• Text Anchor in "/Users/jimmyb/Documents/a-Adobe CC/2026/z-MERGED GUIDE/26-broughtons.indd" is missing: 1
• Text Anchor in "/Users/jimmyb/Documents/a-Adobe CC/2026/z-MERGED GUIDE/26-puget.indd" is missing: 3 T
• ext Anchor in "/Users/jimmyb/Documents/a-Adobe CC/2026/z-MERGED GUIDE/26-sunshine.indd" is missing: 2

I can find nothing wrong with the "Unresolved hyperlinks." They work fine in PDF format.

And the Text anchors are in folders that were long ago deleted.

If you were me, how would you go about your quest to turn this file into a working epub? Thank you in advance for any suggestion you might offer.