I was having problems sending some epubs to my Kindle. I tried following all of the fixes in this thread with no luck. Anyway, for someone who maybe also has this issue on one of their epubs, here's a thread where I described my solution:
https://www.mobileread.com/forums/sh...49#post4242549
Basically, Kindle Previewer was giving me table of contents errors. It turns out the epub's ToC were trying to reference an id in an HTML body tag and the Kindle epub converter didn't like that. So I moved the ids to div tags instead. For example, I started with this in my problem HTML files within the epub:
...
<body id="xxx">
...
</body>
and ended up with this:
...
<body>
<div id="xxx">
...
</div>
</body>
This fixed my very specific problem!