Ok, I'm writing this because I couldn't find a similar problem.
I'm editing in Sigil a book, converted by Calibre from pdf to epub. The book has over 100 chapter breaks, aka .xhtml or .html files (I chose to use chapter break for images to display on separate pages). The chapters themselves, as in TOC are around 40.
Anyway, after I first went over 100 chapterbreaks (that is, 100 .xhtml files) I started having bad problems with the conversion. Pages I introduced at the beginning do not show at all, neither do images. I lost italic formatting all over the book. But this only happens in the mobi format, as viewed by the Calibre viewer, Kindle Previewer, Kindle 4. The epub files (viewed by the Calibre extension) are the way they are supposed to be.
https://www2.mobileread.com/i/smiliesadd1/help.gif
Please. I am losing my mind