It is caused by getting redirected to a page as a result of a 301 status code. The captcha is originally assigned to the 301 request, and a different captcha is displayed after a redirect to 200.

you can test this yourself by going to https://ieddit.com/login instead of

https://ieddit.com/login/

You will be redirected to the url with the trailing slash, and the captcha will fail.

I also plan on modifying the underlying library to avoid using 7s and 1s :)