[tomsem]

I don’t usually use Grid View either, but as an experiment, I switched library to ALL, switched to Grid View, and then navigated to an arbitrary page (tap on the ‘mm of nn’ label in bottom right). Thumbnails appeared within a few seconds for that page and a few pages after that. No need to download the book.

But if an on device item does not have a thumbnail I don’t know if you can trigger download this way. Might be worth removing from device, then see if thumbnail appears in ALL view, then re-download (variation of what others have suggested).

There is some sort of cache for cover images, I would imagine cached images don’t get deleted until some threshold is reached - for example, if you’re running low on disk space, it might be expected to delete thumbnails for items which are no longer on device - but one would have to do some testing to confirm such rules. I’m not curious enough at the moment to undertake such unpaid testing.

In general, I think thumbnails can be generated on-device, even for side loaded items (if item includes a cover image that meets certain magic criteria). But my experiment suggests that downloading thumbnails from Amazon cloud can also happen.