none of the users for your account have two-factor authentication enabled, which is what generates the security codes for signing in and resetting passwords. You can find the option in the My Account section and will have a toggle to enable it.
I disagree. Both of the users on this account are set to require texting a security code to allow a password change.
Also, when I tried to sign in as the secondary user, I got a message that the account had been locked, and I was required to change the password. It did not appear that the password had bee changed, but the account was locked. So the email was completely inaccurate.
I also checked our server and it says Comcast is forcing you to change your password because of it being accessed from multiple countries (UK, Russia, Lithuania, Latin America, etc.). Do you know the last time you ran Anti-Virus and Anti-Malware scans on your devices?