What are the values for global parameters that start with tcp_ in your kamailio.cfg?
``` tcp_connection_lifetime=3605 tcp_rd_buf_size=16384 tcp_conn_wq_max=65536 tcp_accept_no_cl=yes ```
This log should show 5 disconnects. Access to one mongodb-cluster-member (secondary) was blocked right after the start and then unblocked for some more minutes.
[kamailio_bug.log](https://github.com/kamailio/kamailio/files/2224117/kamailio_bug.log)