I have an VXML application in Call Studio which includes a "VoiceXML Insert" element between "CVP Subdialog Start" and "CVP Subdialog Return". Something like : "Start of Call"-> "CVP Subdialog Start" -> "VoiceXML Insert" -> CVP Subdialog Return"

The "VoiceXML Insert" element source is a url to a simple static web application that return the xml content to play an audio file.

Everything is fine, when I call in, I got the sound file played.
The issue is, even I hang up the call after that, the call is still active in VXML server.
Running "<CVP_HOME\VXMLServer\admin>status" the result still shows the call active, and it only got released after the timeout of 30 mins (this is default setting).

It looks like the call got stuck at the "VoiceXML Insert" and never got returned to main flow.
Checking the <CVP_HOME\VXMLServer\applications\<app>\logs\ActivityLog\, the logs has this:
"VoiceXML Insert element name",element,warning,A session has timed out after 30 minutes. This is most likely caused by a start of call class or action element at the top of the callflow not completing before the voice browser's fetch timeout occurred. To resolve it ensure this class executes in a timely manner or run it in the background. Session timeouts may also occur under high load or if there are issues with a load balancer or voice browser.
Any idea how to make the call exit the "VoiceXML Insert" element properly so the session ends immediately?
Much appreciated.