@Hank21 Thanks. It appears the ISP (AT&T wireless) randomly changes the IP address. While the MR5100 stays connected to AT&T (in IP Passthrough), it appears the ER7206 isn't asking for a new IP...

While connected to an ATT Netgear MR5100 modem in IP Passthrough, the ER7206 (after 12-24 hours) will fail the WAN connection with the error "[Named Gateway] failed to obtain the IP address for WAN...