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It’s not just you. Same thing happens to me all the time. At first I thought I may have read them on some other site and thought it was this one until I’d come across ones I KNEW I read on this site and marked as already read and even commented on some but none of that would show up as if I had never done any of that.
I have read mostly mangas whatever it is as long the story is interesting. After reading it, i would mostly marked it as Already Read/Reading now/Want to Read.
But theres something odd that the manga which I've already read and marked it as [Already read] (so that i wont reread it again), and many months later, it suddenly becomes unknown like it was not marked at all.
Is there something wrong with the sites database ? Or may I just the one who experiencing this?