If you have the issue of your devices (especially Macs) picking up the wrong domain suffix during DHCP with your Ubiquity USG gateways, the issue is with USG's implementation.
USG remembers the preferred DNS hostname of local devices as they negotiate DHCP, and records it in its
/etc/hosts file. When clients change their preferred name, USG doesn't seem to respect it, and continues to vendor the previously cached name from
To fix this:
1. Login to your USG gateway via SSH
2. Open its
/etc/hosts file and remove all the cached entries.
3. Reboot USG gateway and force your clients to reconnect and acquire new DHCP leases.