"Most likely a simple failure to follow instructions"
Yikes. The instructions are:
1. Enter User ID and Password.....
2. Enter verification number.
...and in my case unfortunately...
3. Go back to step 1
Not exactly complicated :-)
The only ways to screw up are to take too long to enter the data or to enter the wrong data. In my case neither of these situations applies. If I had continued to follow instructions I'd still sitting typing in my user ID, password and verification number for the umpteenth time.
I'm not suggesting for a minute that it doesn't work for you, I'm sure it does - and probably works fine for the vast majority of others. It just doesn't work for me. Perhaps because I have some weird combination of software releases or hardware; or perhaps because of some bizarre localization or encoding issue; or perhaps because of network issues in my region. Who knows - multi-factor authentication is a hugely complex process to get right.
Anyway, I can see you can't be persuaded that there's an issue so I'll leave you to your devotions. Thank you for your suggestions. I'm sure you're a great help to many.