Every time that Amazon updates their encryption, it takes a little time for Epubor to catch up. Usually no more than a month. Be patient and keep an eye out for the new version.
When you open Epubor Ultimate, there will be a number at the upper right when a new version comes out.
I've tried all the troubleshooting options, but I can no longer convert Kindle books. Paid license just to convert kindle...
Epubor 3.0.16.567
Kindle for PC 2.8.3 (70995)