CAFCASS do make mistakes. Google CAFCASS and you will see the thousands of disatisfied people that CAFCASS has affected their lives and their relationship with their children.
People make mistakes, and CAFCASS are no different. There is only one person that makes a decision in court though, and that is the Judge. The Judge can overule the recommendation made by CAFCASS if you can show a good reason to.
This guide explains what reasons my be worth arguing in your case, and shows how to find mistakes to exploit in your challenge.
The guide also explains how and when to complain, and how to challenge your report in court.