Not on my side. When ever I got the same document inserted twice, it was my mistake. It was due to synchronization issues, wrong logic on my side (ex: wrong query part for an upsert). If you end up with duplicate data it is because your code has added twice.
In your case BookModel.create() is called twice within the same function. Twice within the same with data coming both from req object. The first create uses newBook but newBook is …req.body and the second create uses req.body directly.