To answer your last question first: With the KT3 of my friend both the document (KUAL.azw2) and booklet version (KUAL.kual file) work under 5.8.9. But the other 8th generation's Kindles may vary (like your mileage
...).
@Valladao: Well, looks like you still have the "very first step jb key" which you installed under the initial fw via the ;installHtml command. But unfortunately, the "hotfix" seems to be gone. This hotfix transfers the whole bunch of developer keys into the system partition. That is the prerequisite for
any other apps/hacks to run - except KUAL, and of course the hotfix, themselves.
Have you tried to reinstall the hotfix via the "Update Your Kindle" menu? This should bring the bundle of keys back to your device. And all the other apps/hacks you use will no longer fail due to "missing permissions" (i.e. their respective key isn't on the device yet - just that one used for the hotfix and KUAL is).
Gesendet von meinem Google Pixel mit Yabba-Dabba-Talk.