Webex client initiates STUN messages as RTP keepalive mechanism. These messages are not common in the telco industry and they are creating critical issues to one of our most common CPE vendors, leading to customer service impact. For this reason, we are unable to go-live with the new Webex client since this problem could affect many customers.
It would be logical to have a config option to control whether the Webex client would send STUN messages or not. Please investigate with high priority the inclusion of such parameter in the next official release or patch.