In preparation to calling Spectrum support I did a full power cycle/reset. Now the system is working as expected. Not sure why or what was different this time as I had done all of this several times before. Maybe I didn't wait long enough or didn't follow the exact sequence?
What I did exactly:
Power down the modem.
Disconnect Modem to AXT1800 WAN cable.
AXT1800 Admin panel > System > Reset Firmware.
Wait for Firmware reset to complete with AXT1800 light slow flashing.
Connect to AXT1800 Admin panel, set language and password.
Power up Modem wait for stable condition.
Connect Ethernet cable from modem to AXT1800 WAN port.
Wait for AXT1800 light to go steady.
All connected devices are working as expected.