Folder full of books disappeared from my Max Lumi

I was transferring a bunch of pdf's from my laptop (linux) to my Max Lumi via the usb cable, until I got an error message, something like "cannot write to..." Then when I tried open one of the files on the Lumi, I discovered that my entire Books folder was empty. The folder is still there, but there's not a single file inside. However, the folder and all its contents show up on my laptop when connected with usb. I can right-click on the files and get file info when I click on properties, but I'm not able to open the files. All the other folders on the Lumi are fine, it's just the Books folder that has this issue.

So I'm wondering if there's a way to recover all those pdf's. I have them backed up but there's a lot of them and it would take forever transfer them back on. Firmware is current.