Can't display cover when use kindle browser to download the ebook

Describe the bug/problem I try to download a book and convert it to mobi and azw3, and in the calibre-web can display the cover. But when i use kindle browser to download the file, I can't get it cover, also its title not change as same as the calibre-web

To Reproduce Steps to reproduce the behavior:

1. Go to kindle browser
2. Click on the download button
3. can't display the correct ebook cover and title

Expected behavior the metadata on kindle can be correct

Environment (please complete the following information):

• OS: [e.g. Windows 10/raspian] unraid
• Python version [e.g. python2.7] 3.6.9
• Calibre-Web version [e.g. 0.6.5 or master@16.02.20, 19:55 ]: calibre 4.12.0
• Docker container [ None/Technosoft2000/Linuxuser]:Linuxuser
• Browser [e.g. chrome, safari] kindle browser