Hello. it seems you already have the latest version but a copied file need to be replaced.

You need to go to the files on your server, make a copy of the file packages\two_step_authentication\authentication\concrete\two_step_authentication.php

and put it inside application\authentication\concrete where it will replace the file already there.

You might also have to empty your cache depending on your settings.

Please let me know if that doesn't work for you or if you feel unsure and want me to help perform the modification.

Thank you so much for the speedy reply!

I made this change and that did the trick. I didn't need to clear the cache, but did anyway - just in case for later.

Do you think it was just an issue with the update that wasn't quite right (e.g., bad timing on my updating the your app and concrete updates?)

Either way thank you so much!

A tiny change in the new Concrete CMS broke my package because of a conflicting variable name. So I had to change that variable name.
When you enable 2FA on your site, the package copies 2 files in the application folder. One of them contains the faulty variable name.

Like an idiot, I forgot that I needed to also modify the file already in the application folder.

In future versions, I'll make sure that happens during the updating process to avoid this kind of issue.