Sometimes I get that when it takes too long to load data- I live in an area where the internet connection is frequently slow. When I get the captcha request, I open another window and close the one that wants to verify me. Works okay that way.
I am more likely to get the captcha test if I am traveling. The websites know your IP address and if they also have left cookies they know your computer is in a different area because the IP address changes, for some reason they care. Also if you use a VPN that will change the IP address seen by the website, but the cookies still indicate what computer you are using. The IP addresses used by the VPN are also probably on a list somewhere so websites can tell if you are using a VPN which they don’t like.