1) Set the Core Log Level to DEBUG and save.
2) Edit every SIP profile involved in the issue you are getting logs for and ENABLE SIP TRACE.
3) Go to System->Reports->Network->Network Capture. Then click Capture and reproduce your issue.
See Using Network Capture Filters for more information on how to capture certain packets only.
4) Stop the trace once the issue is reproduced and download the wireshark trace.
5) Go to Backup - Restore, then click Backup.
6) Select Support Backup as the backup type, then click backup and download the backup.
Send in both the Support Backup (from step #6) and wireshark trace (from step #4) to support.