If 2 Factor authentication is enabled on email/SMS:
If the user types in their username and password, and get the one-time code. The code will get sent only the first time.
If the user happens to click the back button, or doesn't complete the authentication, then go back to the login and type in your username and password again, the Onetime code does not get emailed.
The only work around right now, is to either restart the Control service, or ask the user to wait for a while, then try again.
Have the onetime code, ALWAYS send the email, regardless of whether it's been sent 2 minutes ago.
Resend 2-factor code on email/SMS every time
Customer support service by UserEcho