The server they kept the reading list on crashed and they lost all the data. The only ones they were able to recover were series where you rated or added tags on them. They should be in your already read list(I had to switch over some to my reading now list because of this)
A good rule of thumb for now is if you often comment, you can go through your comments and stuff and find stuff you’ve read and re-add them to your list.
If you make lists, the lists should still be available as well.

Give me back my bookmarks...