You might want to try running the EPUB through https://kindle-epub-fix.netlify.app/ https://kindle-epub-fix.netlify.app/ This applies a few fixes for problems

You might want to try running the EPUB through https://kindle-epub-fix.netlify.app/ https://kindle-epub-fix.netlify.app/ This applies a few fixes for problems with EPUBs that the Send to Kindle service doesn't like.