KDP has lately taken to objecting to endnotes (which in my case they referred to as “footnotes” for some reason) that don’t link back to the text. They provide the html code for creating backlinks in their Kindle Publishing Guidelines, but this would require a lot after the fact code tinkering that defeats the purpose of doing an ePub in InDesign. If you have actual footnotes, the ePub export dialog in InDesign lets you specify whether they appear as popups or at the end of a chapter. I haven’t received any negative feedback from KDP about these, but I have about endnotes that I set up as cross-references. There are several ways to get back to the text when viewing an endnote and it varies depending on the Kindle device/app. I did an experiment with a dummy document, creating the backlinks the way KDP wanted them. I didn’t see any difference between these backlinks and what you get when you export an ePub with cross-references. My suggestion is tell KDP the error they are concerned about is not an issue.