When i try to log on to xfinity i've been getting this message "This site is not secure" with error code: DLG_FLAGS_SEC_CERT_CN_INVALID
In case someone else runs into this, another possible cause of the reactivation isste is a DNS configuration problem. My router and Wifi are separate from the modem and they learned the initial DNS servers used for setup/activation from the modem. Normally a reboot would fix this, however I have a bit of a non-standard network setup and this was the cause of the problem. Adding the correct DNS servers for Comcast (188.8.131.52 and 184.108.40.206) resolved my issue. I have an old Aries modem and it works fine.
Dead thread from last year now being closed.