DNS issues with using custom SSID

Came home from a week of traveling to find my phone and bedroom laptop not being able to resolve DNS over WiFi.  Restarted router - CG3000DV2 / N450.  It's worked fine for over a year or so...  Connected work laptop over ethernet and all pages load quickly.  Changed channels on router, "forgot" network on phone, etc.  Finally did a factory reset on router and connected to default SSID.  Internet loaded fine on phone.  WAT.  Then changed the default SSID to a new custom SSID (not the old one). Works fine.  Changed it back to the SSID I had before.  DNS could not resolve.  Again, WAT.  Both SSIDs are not the original SSID.  Both are hidden.  Both are on the same channel.  Why would my router/ISP block one SSID from resolving pages over another?  Any ideas???  I'll stay with the "new" custom SSID but it's definitely annoying.