I face the same problem, and think that I do know why this happens.
The gmail account that I use is normally used from India, and the webserver that I use is located in The Netherlands.
Google notifies that there was a login attempt from am unusualy location and requires to login from that location via a web browser.
Furthermore I had to accept suspicious access to the gmail account via https://security.google.com/settings/security/activity
But in the end my problem is not yet solved, because I have to login to gmail from a location in The Netherlands.
I hope this will help you a little! (sorry, I do not read email replies on this email address)