If the Duet WiFi is out of range of the access point it is configured for, or you turn off that access point, then it will start up in access point mode just like it did when you received it.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].