No Thumbnails/Covers on lockscreen even after STK (Please don't delete)

[maakies]

I just re-read the rules and don't really understand why my thread was deleted about this. I have no private messages helping me understand why. Please let me know what I'm doing wrong, if anything.

As the title says, though I can see covers for only a couple of books (epubs). I've edited meta-data for some of the books via Calibre but that doesn't seem to be related.

I've read a bunch of threads and either there's a long solution that isn't feasible for a library or that people insist send2kindle should work.

Can someone please help?

Thank you