I stumbled on to this when upgrading an old Duet 2 Ethernet from v3.3 to the current 3.5.1. I set up my router to assign a specific IP address to the Duet based on the MAC address and had a slight freak out when the DWC couldn't reconnect to the Duet. Might be worth mentioning on the updating firmware page.
https://docs.duet3d.com/User_manual/RepRapFirmware/Updating_firmware