dhcpd losing hostnames

[Michael Vincent]

A few pfSense 2.3.1 (based on FreeBSB 10.3) users have noticed an
issue with the dhcp server (ISC DHCP Server 4.3.3-P1) losing client
hostnames regularly. Packet captures have proven that while hostnames
are always provided by clients and generally recorded in dhcpd.leases,
the hostnames often disappear from dhcpd.leases after some period of
time. We haven't been able to conclusively prove that dhcpd itself is
to blame, but investigations of packet captures and logs are pointing
in that direction.

Background is available in this thread:
https://forum.pfsense.org/index.php?topic=110011.0 and a bug ticket
has been opened here: https://redmine.pfsense.org/issues/6589

One user installed OPNSense 16.7 RC1 (a pfSense fork) that includes
ISC DHCP 4.3.4 and still experienced the issue. I'm not sure which
version of dhcp was used in pfSense 2.2.6 offhand, but this issue of
missing hostnames was not present there.

One theory I've come up with is that clients that request a lease too
soon after their last renewal (reuse_lease in the logs) cause dhcpd to
lose those clients' hostnames for some reason, but I haven't had a
chance to test that in a controlled way yet.

Is there any way to make the dhcpd logs more verbose? Any suggestions
on debugging techniques or things to try to narrow down this issue?

My dhcpd.conf:

    option domain-name "mydomain";
    option ldap-server code 95 = text;
    option domain-search-list code 119 = text;
    option arch code 93 = unsigned integer 16; # RFC4578

    default-lease-time 7200;
    max-lease-time 86400;
    log-facility local7;
    one-lease-per-client true;
    deny duplicates;
    ping-check true;
    update-conflict-detection false;
    authoritative;
    subnet 192.168.1.0 netmask 255.255.255.0 {
       pool {
           range 192.168.1.100 192.168.1.245;
       }

       option routers 192.168.1.1;
       option domain-name-servers 192.168.1.1;
       default-lease-time 259200;
       max-lease-time 518400;
       option ntp-servers 192.168.1.1;
    }
    host s_lan_0 {
           hardware ethernet 00:00:00:01:01:01;
       fixed-address 192.168.1.2;
       option host-name "StaticClientA";
    }