covers are not showing up when i add books

[Pikachu]

I just added over 50 books and not one had a pic.
I tried different folders same thing
I tried a book that worked before same problem
I went back to 4.19 and same thing. Im back to 4.2
I don't know what to do. I open to a temp folder, sort and fix files, then move them to thier main folder. so i went to the main folder (cooking) and everything there had covers.
If I drag and drop books i know sould have covers like pdf's they don't.
I don't know what to do. It used to work
Oh I rebooted too.
DJ