I'm using bookdown to author a technical book. I've followed the format layed out in the bookdown book very closely and it looks good in epub, html, and pdf versions. I made heavy use of custom blocks to highlight specific kinds of information but when I convert to a .mobi the custom blocks no longer render properly. The icons don't show at all. I've tried converting with kindlegen and with calibre and it is the same.
I downloaded the .mobi version of the Yihui Xie's excellent bookdown book directly from the site and uploaded it to my tablet kindle reader. It shows the same problem. Is this even possible?