Have you had a look at the REST connector log? By default the log is stored in %ProgramData%\Qlik\Custom Data\QvRestConnector\Log.
If you are able to reload successfully manually but not when running from QVS/Publisher, the likely difference is the account being used to run the reload. When you run the reload manually, you are using your own account? When you run the reload from QVS/Publisher, the account being used is the QlikView service account running the QlikView Distribution Services. A test you can try is to login to a computer which has QlikView Desktop installed as this QlikView service account and attempt to run the reload. If it fails, you are likely experiencing a permissions issue with the account.
Hope this helps.
Sr. Technical Support Engineer with Qlik Support Help users find answers! Don't forget to mark a solution that worked for you!