From FreeSWITCH UA to FreeSWITCH Server:

10.250.5.17:5090 -> 10.250.5.50:5090
  INVITE sip:185511@192.168.1.30 SIP/2.0..Via: SIP/2.0/UDP 10.250.5.17:5090;b
  ranch=z9hG4bK.I4KG97dOK;rport..From: <sip:1001@10.250.5.50>;tag=MeYxCN9Lq..
  To: sip:185511@192.168.1.30..CSeq: 20 INVITE..Call-ID: t2XYFvCyYU..Max-Forw
  ards: 70..Route: <sip:10.250.5.50:5090;lr>..Supported: outbound..Allow: INV
  ITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE, SUBSCRIBE, INFO, UP
  DATE..Content-Type: application/sdp..Content-Length: 328..Contact: <sip:100
  1@10.250.5.17:5090>;+sip.instance="<urn:uuid:2f0b19de-2db0-4bef-be7d-48bf48
  3a8141>"..User-Agent: Linphone/3.9.1 (belle-sip/1.4.2)....v=0..o=1001 3679
  1124 IN IP4 10.250.5.17..s=Talk..c=IN IP4 10.250.5.17..t=0 0..a=rtcp-xr:rcv
  r-rtt=all:10000 stat-summary=loss,dup,jitt,TTL voip-metrics..m=audio 7078 R
  TP/AVP 0 8 101..a=rtpmap:101 telephone-event/8000..m=video 9078 RTP/AVP 96
  97..a=rtpmap:96 VP8/90000..a=rtpmap:97 H264/90000..a=fmtp:97 profile-level-
  id=42801F..

10.250.5.50:5090 -> 10.250.5.17:5090
  SIP/2.0 100 Trying..Via: SIP/2.0/UDP 10.250.5.17:5090;branch=z9hG4bK.I4KG97
  dOK;rport=5090..From: <sip:1001@10.250.5.50>;tag=MeYxCN9Lq..To: <sip:185511
  @192.168.1.30>..Call-ID: t2XYFvCyYU..CSeq: 20 INVITE..User-Agent: FreeSWITC
  H-mod_sofia/1.7.0+git~20151211T002348Z~cae255395f~64bit..Content-Length: 0.
  ...

From FreeSWITCH Server to OpenSIPS:

 10.250.5.50:5090 -> 10.250.5.3:5080
  INVITE sip:185511@10.250.5.3:5080 SIP/2.0..Via: SIP/2.0/UDP 10.250.5.50:509
  0;rport;branch=z9hG4bKQ4XSKc0vUp4FD..Max-Forwards: 69..From: "1001" <sip:10
  01@[10.250.5.50:5090]>;tag=2XyUKHFD2y6pF..To: <sip:185511@10.250.5.3:5080>.
  .Call-ID: 65474177-6471-1234-e187-000c295a647b..CSeq: 88639388 INVITE..Cont
  act: <sip:gw+osips@10.250.5.50:5090;transport=udp;gw=osips>..User-Agent: Fr
  eeSWITCH-mod_sofia/1.7.0+git~20151211T002348Z~cae255395f~64bit..Allow: INVI
  TE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTI
  FY..Supported: timer, path, replaces..Allow-Events: talk, hold, conference,
   refer..Content-Type: application/sdp..Content-Disposition: session..Conten
  t-Length: 218..X-FS-Support: update_display,send_info..Remote-Party-ID: "10
  01" <sip:1001@10.250.5.50:5090>;party=calling;screen=yes;privacy=off....v=0
  ..o=FreeSWITCH 1457928161 1457928162 IN IP4 10.250.5.50..s=FreeSWITCH..c=IN
   IP4 10.250.5.50..t=0 0..m=audio 22744 RTP/AVP 8 101..a=rtpmap:8 PCMA/8000.
  .a=rtpmap:101 telephone-event/8000..a=fmtp:101 0-16..a=ptime:20..

U 10.250.5.3:5080 -> 10.250.5.50:5090
  SIP/2.0 100 Giving a try..Via: SIP/2.0/UDP 10.250.5.50:5090;received=10.250
  .5.50;rport=5090;branch=z9hG4bKQ4XSKc0vUp4FD..From: "1001" <sip:1001@[10.25
  0.5.50:5090]>;tag=2XyUKHFD2y6pF..To: <sip:185511@10.250.5.3:5080>..Call-ID:
   65474177-6471-1234-e187-000c295a647b..CSeq: 88639388 INVITE..Server: OpenS
  IPS (2.1.2 (x86_64/linux))..Content-Length: 0....

U 10.250.5.3:5080 -> 10.250.5.50:5090
  SIP/2.0 400 Bad Request..Warning: 399 192.168.1.30 "Malformed headers : Fro
  m "..To: <sip:185511@10.250.5.3:5080>;tag=7ea5fd275b6bfe2bcdd1565b6841ecc6.
  .Call-ID: 65474177-6471-1234-e187-000c295a647b..CSeq: 88639388 INVITE..Via:
   SIP/2.0/UDP 10.250.5.50:5090;received=10.250.5.50;rport=5090;branch=z9hG4b
  KQ4XSKc0vUp4FD..Content-Length: 0....


After that only timeout or cancels ends sending this error.