I personally just switched to my production server when this happened. Because this is a new IP location, Google attempted to protect my account by blocking the sign-in.
To fix this, I followed the steps in this answer:
First, enable access to less secure apps in your Google account here: https://www.google.com/settings/security/lesssecureapps
Since I had already done this, and my problem was now because of a new IP address, I had to manually confirm the next sign-in attempt using this link: https://accounts.google.com/DisplayUnlockCaptcha
See the linked answer for more information.