OK, I get it. USAA is totally freaked out to the point of paranoia over account security.
I have 2 email addresses on my account. Signing in I was sent a security code on email account #1 and I put the code into the space provided to sign in. USAA response was that a code had sent to email#2. Oh, OK, so I input that one as requested. I got a blank screen for my effort. Two attempts to sign in had resulted in two security codes with two ineffective responses from USAA.
So I tried again, this time with email address #2 first. Got the security code as before, input it as before, and was told a security code had been sent to email address #1. I input that one and again got a blank screen for my effort.
Now four attempts to sign in had resulted in four security codes with four ineffective responses from USAA.
USAA's account security is so effective that even a member can not sign in.
FWIW, I use the Symantec VIP Access app that USAA has offered for years. No need for texts or emails, and I have never had a problem logging on with 2-factor authentication -- I just have to have my phone with me. The app also allows me to store 2FA credentials for many of my other logon sites. I have several issues with USAA customer service lately, but logon security isn't one of them.