I’d like to retrieve users data from the the GraphQL API v4 but I have found problems in some cases. For example, the query bellow returns the message  Could not resolve to a User with the login of ‘ReactiveX’ :

{
  user (login:"ReactiveX"){
            name
  }
}

If I use the REST API v3, the data are retrieved normally.

https://api.github.com/users/ReactiveX