Cover thumbnails for Kindle not being generated

Hi,

I wondered why some of my books transfered to my Kindle Paperwhite showed no covers on the device but most did.

I use Calibre's send to device feature (via USB) and as format I always chose AZW3. I also made sure that the "Enable sharing of book content option" is ticked for mobi and AZW3.

As far as I understand the user manual Calibre should then create a cover image thumbnail and place it into the Kindle's system\thumbnails folder.

See: https://manual.calibre-ebook.com/faq...droid-ipad-etc

However during the sending of the file sometimes no new image file is being generated in the Kindle's thumbnails folder. For most books a new thumbnail is placed there and the Kindle shows the cover correctly.

Any ideas on this? Any logging I could enable to investigate?

I'm using the latest version of Calibre.

Tim