I missed those attachments, anyhow next time use ngrep, because the output from wireshard adds too much noize. You can use ngrep to dump the text format from pcap (which can be exported from wireshark), like:
``` ngrep -qt -W byline -I file.pcap ```
The issue is not with via headers at all. The replies are routed properly, there is an ACK following the 200ok.
The problem is routing the ACK. Are you using set_contact_alias() or add_contact_alias()? You should use the first one. If you do it, then there might be some logic error in kamailio.cfg.