LogLevel debug2 handshake logging only on some logins, not on every login of a user

[Hildegard Meier]

> 2)  Is syslog-ng configured to relay the data? If yes, and using UDP,
> 	some log entries might simply be missing because of congestion.

I log locally, the syslog-ng config is plain simple:

source s_src {
       system();    # this is /dev/log on Linux
       internal();  # this is only for error messages from syslog-ng itself
};

filter f_local2 { facility(local2); };  # sshd is configured with "SyslogFacility local2"

filter f_ssh_auth_wanted {
    not level(debug)
    or  message("^debug2: MACs ctos: ")
    or  message("^debug1: kex: client->server cipher: ")
    or  message("^debug2: KEX algorithms: ")
    or  message("^debug2: host key algorithms: ")
    or  message("^debug1: kex: host key algorithm: ")
    or  message("^debug2: ciphers ctos: ");
};

destination d_ssh_auth {
    file("/var/log/app/ssh/auth.log" flush_lines(10) );
};

log {
    source(s_src);
    filter(f_local2);
    filter(f_ssh_auth_wanted);
    destination(d_ssh_auth);
};

# delete all other unwanted sshd debug messages (no destination = no action = "delete")
log {
    source(s_src);
    filter(f_local2);
    flags(final);
};

I have no clue why the debug messages that match on the filter (e.g. "debug2: host key algorithms: ssh-rsa,ssh-dss [preauth]") are only logged _sometimes_ in /var/log/app/ssh/auth.log and not together with every "Accepted password" log entry.