Qlik Support does not support customization of AccessPoint. In order to rule out that the customization is responsible for the behavior perform either one of the following:
Setup QlikView WebServer (QVWS) or non-customized AccessPoint via IIS.
Rename the C:\Program Files\QlikView\Web folder and replace it with one from a standard installation
Note: Ensure that the /QvAjaxZfc and /WebTicketSite web sites are using the "QlikView IIS" Application Pool and not the DefaultAppPool.
If issue does not occur with a default AccessPoint install the customization needs to be investigated as the root cause.