Hi everyone,
I’ve compiled my novel and the cover image shows when you are reading the book in kindle. But when you are viewing all of your books, the novel cover doesn’t show. Just a gray box.
I tried a totally different cover from another book and it worked!!?? Does anyone have a solution to this?
thanks,
Dave
SOLVED: I changed my cover image to 844x1214 pixels and it went in fine.
I’d take a look at the two cover files, the one that didn’t work and the one that did, with an image editor or viewer that can show you file format, bit depths, color space and so on. I’d also check for file size, if the cover image is massive that might impact thumbnail generation. So in addition to making the file formats and details as close as you can, size and DPI can also matter.
That aside, I am aware of an issue with some devices when it comes to displaying the type of Mobi file that kindlegen produces. It’s a hybrid, with both legacy and modern formats embedded with in it, just what you need for something you’re going to upload to Amazon for sale through their system. Otherwise it’s not, strictly speaking, a to-spec .mobi file, so support of it can be spotty.
That doesn’t sound like what you are seeing though, given it worked with a different image.
One last thing to be aware of: most of the reader software and devices are tuned for readers, not producers, surprise. 
They have a preference for caching cover art instead of regenerating it. Changing the meta-data for each incremental test should dodge that problem easier than finding a way to reset the cache, when it happens.
Update: Oops, saw your update after I posted.