Hi,
I transferred the .mobi ebook from my PC to tablet via Calibre.
Now in the books section on my Kindle it displays the cover just fine but not on the carousel.
Have a look (it's the book called 'Monster Blood'):
http://i.imgur.com/OXrX1lf.png
http://i.imgur.com/mE1t4vT.png
After converting mobi to mobi:
http://i.imgur.com/WlQ62TK.png
http://i.imgur.com/AaGBk6z.png
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I did search around a bit to see if I can find a solution, the two I came across were updating the metadata to include the ISBN and converting it from mobi to mobi. Well the metadata appears to be fine, ISBN is present.
And converting from mobi to mobi didn't solve it.