Troubleshooting Books not showing up on library (but they are on device)

[doedeer]

Over the years I have sent hundreds of books to my kindle using Calibre. Usually download .epub, add it to my calibre library, connect my kindle via USB and then convert and send to device. Lately, when I send a book it doesnt show on my kindle's library. If I use the search function, I can find them and read it, so the conversion and connection went fine, it just doesn't appear in the libary.

Some things I tried:
1. restarting my kindle.
2. converting to azw instead of mobi.
3. many different files.
4. deleting files that show on my library, and then re-sending them again (they don't show).


I'm using Calibre 6.7.1. I have a 6th gen kindle paperwhite (Firmware 5.12.2.2), it's been on airplane mode for many months now.