They aren't anonymous. Its the site's bot.
What the bots trying to do?
Oh yeah I’ve seen this issue a lot! Idk why? However, I saw other uploaders place a “placeholder” after the last chapter they put up, as to stop these bots from re-uploading the chapters. Try doing that~
Thank you for uploading and fixing broken pages. Much appreciated. :)
I think when only the first page is uploaded its cause the bot can't read the following format of the next pages (I might be wrong though), so it uploads only what it can.
It's happen again, who uploaded it? It's an anonymous uploader. I think it happened before where they didn't post the chapter :/