Captcha not Working

Hi guys, I started using sci hub yesterday and I´ve found it pretty amazing so far but I have some issues with the captcha when I try to download some papers, since the captcha doesn´t pop up in every one of them. When it happens, I type the word and it always give me another captcha to fill in, if anyone knows why is this happening and how to solve it I´d be very grate ful. I´m using []( with the chrome extension btw.