iPhone SE DHCP problem with iOS 12.0.1?

My iPhone SE has suddenly stopped receiving an IP address from my dhcp server when it connects via WiFi. The only recent change that I can think of is that the phone upgraded to iOS 12.0.1.

Other devices (Android phones, Windows desktops and my iPad 2018 using iOS 11.4.1) connecting via WiFi have no problems getting an address and accessing the internet. It is as if the DHCP request, if sent, never reaches my DHCP server (Windows 2008 R2). The iPhone assigns an automatic address (169.254.x.x). Renew Lease doesn't do anything visible. For the 2 years prior my iPhone SE had no problems. My WiFi is provided by a Linksys WRT3200acm linked to a Comcast router in bridge mode. The DHCP server connects to the Linksys router. This environment has been unchanged in several years. The same phone can get IP addresses when connecting to other networks, and if I assign a static IP on the phone it operates normally on my network. It seems to me to be some sort of incompatibility between the phone and my Windows dhcp server. Anyone got any ideas how to diagnose and fix this?