To ensure a high bar of security and privacy, we use Google’s Re-CAPTCHA software. Due to this, there might be times when you try to sign in that you must check or complete multiple CAPTCHA attempts. Don’t worry, this is totally normal. Once Google recognizes your email as a valid and safe email it will not require the CAPTCHA verification.
CAPTCHAs can be caused by a variety of reasons including: when a browser that may be a bot is detected, when a user attempts to login from an IP address with a poor reputation (VPN's, Tor, bot-nets, etc.), or after rapid succession login attempts.