I think it's my fault. Maybe it's because I use AdGuard DNS. Let me try deactivating it.
Edit: Still zero star on PC with none of the default settings changed (usually I use mobile). Well, it's fine since it doesn't obstruct the reading experience.
I forget to rate the stars for a review. I edited it and rated 5-star. But when I came back and see the review, my review's star rating is still empty. I repeated it many times but the stars won't change. I feel bad for for giving no star even though his novel is so good.