pfSense

In a HA setup with DHCP server enabled, both peers will assign IPs. The leases that sync to peers don't include client-hostname. Where DHCP registration to DNS is enabled, each system in a pair only knows the hostnames for leases it issued, leaving name resolution of DHCP hostnames about 50% broken (half will work on the primary only, other half work on the secondary only).

a dead-end discussion of this issue:
https://lists.isc.org/pipermail/dhcp-users/2009-February/008329.html

dhcpd likely needs fixed.

This is something that will almost certainly be post-2.2, but putting to 2.2 for the moment in case we can find a quick fix.