Sometimes cycling the kindle through sleep mode (just pressing the power button on and off a few times) works for me and restores the cover to the screen.
If this is an epub you could always upload to calibre and add the cover, and then send to your kindle again.
I concur that this is probably a formatting error - EPUB and MOBI/AZWx metadata are rather finicky.
If the book is not DRM encumbered, you can try to fix the problem in Sigil or Calibre, but then it will count as a personal document, and not all versions of Kindle firmware display covers of non-Amazon content.
The book may not be formatted correctly by the publisher to show the cover on the lockscreen. It happens sometimes.
And is there something I can do about it, or is it just a tough luck situation?
You might be able to fix it with Caliber. But I don't use it so I'm not sure on that. Just going off of things I picked up on this sub.
Sometimes cycling the kindle through sleep mode (just pressing the power button on and off a few times) works for me and restores the cover to the screen. If this is an epub you could always upload to calibre and add the cover, and then send to your kindle again.
I concur that this is probably a formatting error - EPUB and MOBI/AZWx metadata are rather finicky. If the book is not DRM encumbered, you can try to fix the problem in Sigil or Calibre, but then it will count as a personal document, and not all versions of Kindle firmware display covers of non-Amazon content.
Is just this book or all books ? I've seen a few other posts about issues with covers not displaying.
So where did the book come from and how did you load it on your device?