Are anybody experiences issue when for some of calls  ACK send to other IP.
http://prntscr.com/jtxkbz
in this case FS in bypass media with two profiles (1 to internet, 2 intranet).
INVITE is send to DNS name that is resolved to
  1. 10.0.9.32
  2. 10.0.9.33
  3. 10.0.9.34
  4. 10.0.9.35
FS 1.6.19

Contact on 200 message is correct

SIP/2.0 200 OK Via: SIP/2.0/TCP 10.0.9.51:12000;rport=39049;branch=z9hG4bKBH60NQjSZj36a From: "Anonymous" <sip:+12022553656@10.0.9.51>;tag=rH5cBQarr559D To: <sip:13013688630@metropolis.ack.one>;tag=UDv7UXv3B53Da Call-ID: b0e4d7e1-e79e-1236-8cb9-02420a000933 CSeq: 123998414 INVITE Contact: <sip:13013688630@10.0.9.33:11000;transport=tcp> User-Agent: proxy.ackone.com Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY, PUBLISH, SUBSCRIBE
Now for future investigate FS upgrader to 1.6.20 and enabled siptrace and loglevel

Sergey Safarov