They aren't deleted you'll get them back.
don't worry, ppl whose acc were made in 2014 and 2015, as in earlier years, they're slowly getting their reads back. Here's some proof
https://www.mangago.me/home/people/65330/home/
https://www.mangago.me/home/people/7934/home/
https://www.mangago.me/home/people/12004/home/
so yeahh it'll take quite some time but you'll get them back.
also once they're back, in case you're looking for ways to save them perhaps in an excel file, I've made a tutorial on how to do it easily and quickly rather than having to enter everything manually one by one, so if you'd like, you can check it out.
https://docs.google.com/document/d/14Drj0CviUhrAmZlU-DC-AtxGFQoH1_PYQ81b2Vzu82w/edit?tab=t.0
im guessing anywhere from a day to a whole week cuz the way they're adding back stories isn't like instant, they're adding it back one by one so when you'll see the date the story was added in your list, it'll show present date, and they're starting with 2014 users so it'll take quite a long while for them to get till new gens

Yooo im going crazy where's all my recorded manga?! My reading, already reading, want to read manga library?!!! Its already reached thousands and suddenly just turned to 0?!!!!! Mangago what's going on???!!