Some, but not all, RW phones stopped receiving the Two Factor Authentication (2FA) codes required to sign onto individual mySocialSecurity accounts during early November, 2019. When trying to access your account at ssa.gov/myaccount the code required to complete signon is not received as a text message. The SSA page implies that a code (fresh security code required every time you access your online account) may also be received via email, but: the only way to add (or change to) email as an authentication channel is by requesting a new account activation code sent to your snail mail address, in 5-10 business days. Yes, SSA has your email and is sending notices to that email, but to get logged onto MySocialSecurity will take waiting for an account reset code via postal mail.
When you try to log onto your SSA account and don’t receive a text from short code 79913 with the required 2FA code in a few minutes, you will need to choose the SSA page option declaring that your mobile phone number “is no longer available” to you. Then you will be advised that you must request a new activation code via snail mail, to arrive in 5-10 business days. This is the confusing point, only by going through a process similar to that when first signing up for SSA online access can we change to having 2FA via email. Then when going through the account activation / reset process you will see that your mobile number has been erased from your SSA profile, so add it back in, if you hope to use text messaging for 2FA in the future. But also request that 2FA (or Multifactor Authentication (MFA) as SSA calls it) be done via email for the interim!