All my PDFs/EPUB/MOBI format eBooks are corrupted. 8 GB worth of my collection is completely ruined.

I’m absolutely disappointed. I’ve been carefully saving my entire book collection here, and now when I try to access the files after some time, they just keep loading and eventually show a blank page.

I tried downloading them in the local and opening them again — same result.

Recently, I used WebDAV on the Documents app (iOS) and got a message saying the file is corrupted.

Could someone help me understand what might have gone wrong? Is there any way to recover these files, or is everything lost? :(

Error screenshot in Documents app

in nextcloud app

Note: I’m using https://nd.nl.tab.digital/ — it’s one of the official Nextcloud providers.