Not Enough Time
When you are asked to enter the code when logging in on a device, getting the code from the app resets you back to the email entry.
If you open the app first and quickly write down the code, you dont have time to enter a long email or password before the code resets.
I deleted the app and went back to text message codes instead that appear at the top of the browser. They stay on the screen long enough to remember and enter without resetting the logging in.
Beartalon about
Google Authenticator, v3.0.0