Looking at the SIP logs from one of the phones. The call was still ringing yet there was a CANCEL message that came through. Here is the log:
1182414.546|sip |3|00|New Connection Accepted
1182414.546|sip |0|00|Plcm Socket created 0x43002f38
1182414.547|sip |1|00|Task name tTCPListen227
1182414.547|sip |1|00|MsgSipTcpAccept
1182414.547|sip |1|00|socket accepted 34500712
1182414.547|sip |3|00|Waiting for a New Connection 0x42703cb8 0x42703dc0
1182414.547|sip |0|00|RecvThreadLocal : Invoking ListenForIncomingData()
1182414.547|sip |3|00|Creating recv Thread
1182414.547|sip |3|00|Waiting on recv Thread
1182414.547|sip |0|00|<<< Data received TCP
1182414.547|sip |0|00| Record-Route: <sip:172.20.0.2:5060;lr;sipXecs-CallDest=AL%2CINT;sipXecs-rs=%2Aauth%7E.%2Afrom%7EMWMzNjgxODg1ODg%60.900_ntap%2Aid%7EOTM2NS05MTQ%60%2115d6b2268963f3e08e083c7885ce7bf5>
1182414.547|sip |0|00| Via: SIP/2.0/TCP 172.20.0.2;branch=z9hG4bK-XX-2c45BmKSdwx_v9RibkTfGXb5ww
1182414.547|sip |0|00| Via: SIP/2.0/TCP 172.20.0.2;branch=z9hG4bK-XX-2c36bM8gnCtbAJFUJilABnPd_A~vkb`ZU7Fe6PPrksIEnN0sQ;id=9365-914
1182414.547|sip |0|00| Via: SIP/2.0/TCP 172.20.0.2;branch=z9hG4bK-XX-2c25dp8x9EcsR6V28SvrCKqTTA~ylA2BaASs`BZOdeoBnOQZg
1182414.547|sip |0|00| Via: SIP/2.0/TCP 172.20.0.65:5060;branch=z9hG4bKac369211019;alias
1182414.547|sip |0|00| Max-Forwards: 16
1182414.547|sip |0|00| Cseq: 1 INVITE
1182414.547|sip |0|00| Contact: <sip:
6205551212@172.20.0.65:5060;transport=tcp;x-sipX-nonat>
1182414.547|sip |0|00| Supported: em,100rel,timer,replaces,path,resource-priority,sdp-anat
1182414.547|sip |0|00| Allow: REGISTER,OPTIONS,INVITE,ACK,CANCEL,BYE,NOTIFY,PRACK,REFER,INFO,SUBSCRIBE,UPDATE
1182414.547|sip |0|00| User-Agent: Mediant 1000 - MSBG/v.6.60A.281.003
1182414.547|sip |0|00| Content-Type: application/sdp
1182414.547|sip |0|00| Content-Length: 250
1182414.547|sip |0|00| Date: Tue, 11 Jun 2019 14:40:31 GMT
1182414.547|sip |0|00| Expires: 240
1182414.547|sip |0|00| X-Sipx-Authidentity: <
sip:19...@hutchgov.com;signature=5CFFBD5F%3Ab5399cb00d8cd272ec960f15d1226060>
1182414.547|sip |0|00| X-Sipx-Handled: X172.20.0.2-70.167.36.202
1182414.547|sip |0|00|
1182414.547|sip |0|00| v=0
1182414.547|sip |0|00| o=AudiocodesGW 366968663 366968634 IN IP4 172.20.0.65
1182414.547|sip |0|00| s=Phone-Call
1182414.547|sip |0|00| c=IN IP4 172.20.0.65
1182414.547|sip |0|00| t=0 0
1182414.547|sip |0|00| m=audio 8250 RTP/AVP 0 8 96
1182414.547|sip |0|00| a=ptime:20
1182414.548|sip |0|00| a=sendrecv
1182414.548|sip |0|00| a=rtpmap:0 PCMU/8000
1182414.548|sip |0|00| a=rtpmap:8 PCMA/8000
1182414.548|sip |0|00| a=rtpmap:96 telephone-event/8000
1182414.548|sip |0|00| a=fmtp:96 0-15
1182414.548|sip |1|00|MsgSipTcpPacket
1182414.549|sip |3|00|CStkDialog::CreateRouteSet: transport set to top route 'TCP'
1182414.549|sip |3|00|CStkDialog::SetAddressLocal localTag set to ''
1182414.549|sip |3|00|CStkDialog::SetAddressLocal new address added of 1
1182414.549|sip |2|00|CStkDialog::CStkDialog SetAddressLocal from pRequest To: 'Animal Shelter' <
19...@hutchgov.com:0>
1182414.550|sip |2|00|CStkDialog::CStkDialog SetAddressLocal Config 'Animal Shelter' <
87...@hutchgov.com:0>
1182414.550|sip |2|00|CStkDialog::CStkDialog TAG 'F78C3693-75C14468' generated
1182414.550|sip |2|00|CStkDialog::CStkDialog local addr 'Animal Shelter' <
19...@hutchgov.com:0> Tag 'F78C3693-75C14468'
1182414.550|sip |2|00|CStkDialog::CStkDialog exit 0x1bfd578 local list size 1
1182414.550|sip |2|00|CLocalIPManager::GetLocalIP Local IP identified is 172.20.4.70 for Remote address 172.20.4.70
1182414.550|sip |1|00|SetCallAppearance m_nCallIndex 0 nCallAppearance 0
1182414.550|sip |2|00|CCallBase::IsChallenged COPIED Dialog Tag to pRequest 'F78C3693-75C14468'
1182414.550|sip |2|00|CCallBase::IsChallenged 'INVITE' Dialog Tag 'F78C3693-75C14468' pRequest Tag 'F78C3693-75C14468' state 'Trying'
1182414.550|sip |2|00|new UA Server INVITE trans state 'proceeding', timeout=0 (0x40f04468)
1182414.550|sip |2|00|CStateInviteServer::CStateInviteServer() Entrance
1182414.550|sip |2|00|CStateInviteServer::CStateInviteServerHandler m_bIsRemote:0 m_bFederationType:0 m_bIsBypassEnable:0
1182414.550|sip |2|00|Bypass Disabled, Choosing Application SDP
1182414.551|sip |2|00|CLocalIPManager::SelectMediaIP, Looking for IP for Addrtype: 2
1182414.551|sip |2|00|CLocalIPManager::SelectMediaIP, Addresses: 172.20.4.70 Addrtype: 2
1182414.551|sip |2|00|CStkCall::VoiceFmtpReadLine: Matched i=0, j=0, payload=0
1182414.551|sip |2|00|CStkCall::VoiceFmtpReadLine: Matched i=1, j=1, payload=8
1182414.551|sip |2|00|ParseVideoFmtp, newVideoCnt (0)
1182414.551|sip |2|00|CLocalIPManager::SelectMediaIP, Looking for IP for Addrtype: 2
1182414.551|sip |2|00|CLocalIPManager::SelectMediaIP, Addresses: 172.20.4.70 Addrtype: 2
1182414.551|sip |2|00|CStkCall::VoiceFmtpReadLine: Matched i=0, j=0, payload=0
1182414.551|sip |2|00|CStkCall::VoiceFmtpReadLine: Matched i=1, j=1, payload=8
1182414.551|sip |2|00|CStateReInviteClient::SendResponse response Number = 100, nSubReason = -1
1182414.551|sip |1|00|CStkDialog::SetDialogState: Dialog 'id04990361' State 'Trying'->'Early'
1182414.552|sip |1|00|doDnsListLookup(tcp): doDnsSrvLookupForARecordList for '172.20.0.2' port 45502 returned 1 results
1182414.552|sip |1|00|doDnsListLookup(tcp): result 0 '172.20.0.2' port 45502 isInBound 0
1182414.552|sip |1|00|doDnsListLookup(tcp): doDnsSrvLookupForARecordList for '172.20.0.2' port 0 returned 1 results
1182414.552|sip |1|00|doDnsListLookup(tcp): result 0 '172.20.0.2' port 0 isInBound 0
1182414.552|sip |2|00|CUser::GetFailBackMode 'Timeout'
1182414.552|sip |1|00|CTrans:: SendCommand | this=0x40f04468, bVQMonMessage=0, m_pCall->m_pUser->m_bOBFailOverReRegOn=0, m_pCall->m_pUser->m_bVQMonFailoverEnabled=1
1182414.552|sip |1|00|Send: (TCP) entry for address 172.20.0.2 port 45502 can Connect 0 canFailOver 1
1182414.552|sip |1|00|Send: (TCP) address 172.20.0.2 port 45502 can Connect 0
1182414.552|sip |0|00|IsThisSocket : Found Socket (227)
1182414.552|sip |0|00|Send : Found Socket (227)
1182414.553|sip |0|00| SIP/2.0 100 Trying
1182414.553|sip |0|00| Via: SIP/2.0/TCP 172.20.0.2;branch=z9hG4bK-XX-2c45BmKSdwx_v9RibkTfGXb5ww
1182414.553|sip |0|00| Via: SIP/2.0/TCP 172.20.0.2;branch=z9hG4bK-XX-2c36bM8gnCtbAJFUJilABnPd_A~vkb`ZU7Fe6PPrksIEnN0sQ;id=9365-914
1182414.553|sip |0|00| Via: SIP/2.0/TCP 172.20.0.2;branch=z9hG4bK-XX-2c25dp8x9EcsR6V28SvrCKqTTA~ylA2BaASs`BZOdeoBnOQZg
1182414.553|sip |0|00| Via: SIP/2.0/TCP 172.20.0.65:5060;branch=z9hG4bKac369211019;alias
1182414.553|sip |0|00| CSeq: 1 INVITE
1182414.553|sip |0|00| Record-Route: <sip:172.20.0.2:5060;lr;sipXecs-CallDest=AL%2CINT;sipXecs-rs=%2Aauth%7E.%2Afrom%7EMWMzNjgxODg1ODg%60.900_ntap%2Aid%7EOTM2NS05MTQ%60%2115d6b2268963f3e08e083c7885ce7bf5>
1182414.553|sip |0|00| User-Agent: PolycomVVX-VVX_500-UA/5.9.2.3446
1182414.553|sip |0|00| Accept-Language: en
1182414.553|sip |0|00| Content-Length: 0
1182414.553|sip |0|00|
1182414.553|sip |0|00| Send : >>> End of data send
1182414.553|sip |1|00|CPlcmSipTcpSocket::Send TCP queuedTxData = 0 TotalLen 892 loop count 1 maxQueueDepth 40000
1182414.553|sip |3|00|CStkCall::NewCallState 'Unknown'->'Offering' (0x1bd2c38) m_hUI((nil)),Control Channel(0), ResponseCode(-1)
1182414.554|sip |3|00|Use common source preference for incoming and outgoing calls
1182414.554|sip |0|00|[CCommand::NeedToProcessCID] cmdType = 0 cmdMessage = 0 g_csSipRequestSourceMessage = -1 g_csSipResponseSourceMessage = -1---
1182414.554|sip |3|00|GetRemotePartyAddress from 'From'
1182414.554|sip |2|00|CStkCall::OnEvSubmitDest CallIdType(1)
1182414.554|cfg |5|00|Prm|Array parameter reg.x.telephony index 269 is out of range
1182414.555|cfg |5|00|Prm|2DArray parameter reg.x.server.x.specialInterop index 269 1 is out of range
1182414.555|cfg |5|00|Prm|2DArray parameter reg.x.server.x.specialInterop index 269 2 is out of range
1182414.555|cfg |5|00|Prm|2DArray parameter reg.x.server.x.specialInterop index 269 1 is out of range
1182414.558|sip |3|00|Waiting on recv Thread
1182414.600|sip |0|00|<<< Data received TCP
1182414.600|sip |0|00| Cseq: 1 CANCEL
1182414.600|sip |0|00| Max-Forwards: 20
1182414.600|sip |0|00| Via: SIP/2.0/TCP 172.20.0.2;branch=z9hG4bK-XX-2c45BmKSdwx_v9RibkTfGXb5ww
1182414.600|sip |0|00| Content-Length: 0
1182414.600|sip |0|00|
1182414.600|sip |3|00|Waiting on recv Thread
1182414.605|sip |1|00|SetCallAppearance m_nCallIndex 1 nCallAppearance 1
1182414.605|sip |2|00|SipOnEvCallNewState 0x1bd2c38,0x1e513e0 1,(null), ResponseCode:-1
1182414.611|sip |1|00|[MS-CALL-PARK]: NO PARK OPTION for 0x1bd2c38
1182414.611|sip |2|00|CStkCall::ExtractAocBodyAndSend: IMS/AOC not enabled
1182414.611|sip |1|00|MsgSipTcpPacket
1182414.612|sip |2|00|active dialog after UPDATE being set here, m_pActiveDialog=0x1bfd578,this=0x1bfd578
1182414.612|sip |2|00|new UA Server Non-INVITE trans state 'callingTrying', timeout=0 (0x40f077e8)
1182414.612|sip |3|00|UA Server Non-INVITE CANCEL trans state 'callingTrying'->'completed' by 200 resp 65 timeout(0x40f077e8)
1182414.612|sip |1|00|CStkDialog::SetDialogState: Dialog 'id04990361' State 'Early'->'Terminated'
1182414.612|sip |1|00|doDnsListLookup(tcp): doDnsSrvLookupForARecordList for '172.20.0.2' port 45502 returned 1 results
1182414.612|sip |1|00|doDnsListLookup(tcp): result 0 '172.20.0.2' port 45502 isInBound 0
1182414.613|sip |1|00|doDnsListLookup(tcp): doDnsSrvLookupForARecordList for '172.20.0.2' port 0 returned 1 results
1182414.613|sip |1|00|doDnsListLookup(tcp): result 0 '172.20.0.2' port 0 isInBound 0
1182414.613|sip |2|00|CUser::GetFailBackMode 'Timeout'
1182414.613|sip |1|00|CTrans:: SendCommand | this=0x40f077e8, bVQMonMessage=0, m_pCall->m_pUser->m_bOBFailOverReRegOn=0, m_pCall->m_pUser->m_bVQMonFailoverEnabled=1
1182414.614|sip |1|00|Send: (TCP) entry for address 172.20.0.2 port 45502 can Connect 0 canFailOver 1
1182414.614|sip |1|00|Send: (TCP) address 172.20.0.2 port 45502 can Connect 0
1182414.614|sip |0|00|IsThisSocket : Found Socket (227)
1182414.614|sip |0|00|Send : Found Socket (227)
1182414.615|sip |0|00| SIP/2.0 200 OK
1182414.615|sip |0|00| Via: SIP/2.0/TCP 172.20.0.2;branch=z9hG4bK-XX-2c45BmKSdwx_v9RibkTfGXb5ww
1182414.615|sip |0|00| CSeq: 1 CANCEL
1182414.615|sip |0|00| User-Agent: PolycomVVX-VVX_500-UA/5.9.2.3446
1182414.615|sip |0|00| Accept-Language: en
1182414.615|sip |0|00| Content-Length: 0
1182414.615|sip |0|00|
1182414.615|sip |0|00| Send : >>> End of data send
1182414.615|sip |1|00|CPlcmSipTcpSocket::Send TCP queuedTxData = 0 TotalLen 410 loop count 1 maxQueueDepth 40000
1182414.615|sip |2|00|CTrans::InitRetrans for UA Server Non-INVITE CANCEL state 'completed' Server 2 of 2 (0x40f077e8)