Have power cycled, even completely disconnecting gateway from EVERYTHING and holding reset button in for 2 minutes while disconnected and during bootup (no battery coz no phone service). Cannot access admin tool with default settings and I've never been able to get in to change settings since day one, well over 6 months ago. While viewing device info/settings on My Account app I noticed the 2.4GHz password was no longer the default (5.0GHz remains default). I use both Blur and Last Pass to create and manage passwords. As there is no entry in either of those I know without a doubt I did not change my wifi passphrase, nor my admin tool credentials.
===>SEE UPDATE<===I am also unable to change the wifi passphrase using My Account app. After generating a "very strong password" including ".-," I tap <Save> and nothing happens. I'm assuming the app and the gateway 3 DPC3941T will accept those characters as the current wifi passphrase/password has a "-" in its structure. I even instructed the My Account app to reset my modem, which changed nothing.
Any pertinent advice would be greatly welcomed and appreciated. Cheers.
===> Found a "troubleshoot" button under "Manage My Services" on comcast.com; WiFi password successfully changed! All wireless devices are now connected. Kudos to Comcast for the little yellow button. Made a meticulous re-check of both password managers. I have no record of the former password creation.
===> Still unable to access admin tool through PC or mobile; only managed password I have is the default.
Have you tried a wired connection to a pc to get to the admin tool? I'd try that and maybe a factory reset from there pressing the reset button for 30 secs.. If that doesn't work I'd be thinking of going to swap the device for an Arris TG1682G.