T48G Phones not disconnecting on Auto Answer for Intercom

[telone]

2-T48G running software 35.73.0.50
We have a site running 6-12-65-27 vs 12.0.63
Have 2 stations with Yealink T48G phones both set to Internal Auto Answer=Intercom and not all the time but most of the time the connection remains open even if one of the station ends the call.
The most recent calls show 17 minutes and 22 minutes of activity in CDR when I look at the PCAP they both show that the RTP Stream ends 266 and 301 seconds sooner then the last SIP Packet.
We have other VPS running the same 6-12-65-27 software and Yealink phones with out this problem ?
As a FYI this site has a Sonicwall Router ( managed by the company IT company) we had many issues and have been able to resolve some but this seems to come back .
I changed the conference room setting to =app_meetme CDR show ConfBridge and *80xxx ( ext number)
The problem that is reported is always between the same 2 extension.
Any help on this would be greatly ap preciated
Thanks