Once a call is answered FreeSWITCH sends a 200 OK SIP message to your Kamailio loadbalancer. As per the SIP spec your kamailio box should respond to a 200 OK with an ACK. The FS logs show that it never receives an ACK, and it repeatedly tries sending the 200 OK with no response. After 30 seconds without an ACK FS will assume the call has failed and hangup.
Looking at your Kamailio SIP logs you can see the 200 OKs getting through okay, and no attempt to send an ACK back to FS. I think this indicates an issue with your kamailio.cfg rather than FreeSWITCH.