Hello. I don't know if this answers your question, but sometimes there are scholars who act as editors in (so-called) edited volumes, where several scholars contribute by writing a single chapter.

Dear Patrizia,

Thank you for answering. No, that's not the case here.... It really concerns normal chapters in a volume written all by myself.... Strange isn't it? Can you perhaps find another reason?

Thank you in advance, Guus

I would guess that it could be people who have gotten used to the edited book and believe that all books follow that format, whether the authors are acknowledged or not. Or maybe they just don't believe that two rather different chapters could be written by the same person. Or maybe it's something from fiction, where groups of authors sometimes create an avatar author. Or maybe they are just MAGA supporters for whom the truth is never out there and nothing can be trusted except Q - the other type of AI, Astonishingly Ignorant.