Hi @scottblackburn,
If I understand correctly, you are using MAAS with an external DHCP. Could you take a look to the troubleshooting documentation? Specifically this section:
https://maas.io/docs/how-to-troubleshoot-common-issues#external-dhcp-configuration
In addition to that, you might also find useful this video published not long time ago here in Discourse about how to use external DHCP with MAAS: