Good to know. It actually would not boot to OpenWRT with the WAN RJ-45 disconnected but I'm hesitant to retest. I changed my email and I need to focus on updating my financial accounts, open source forums and contacts. I'm willing to retest after all that is taken care of. There were a number of other users - another user with the same behavior would be strong evidence of a bug and not just a Spectrum DHCP server quirk.
Found more of the same:
https://forum.openwrt.org/t/openwrt-wan-just-wont-talk-to-modem-reason/71295/15
https://forum.openwrt.org/t/strange-ethernet-bug-with-mt7621-device/115279/2
https://docs.openwrt.melmac.net/luci-app-advanced-reboot/
https://forum.openwrt.org/t/redmi-ac2100-dsa-and-cable-modem-no-dhcp-answer/104273