There’s errant code in your site that’s misusing the login_redirect filter. It keeps appending the same URL to the existing redirect, causing an infinite loop that’s only terminated once the URL becomes too long.
You need to disable all plugins and your current theme via FTP. Rename the plugins folder in /wp-content/ and your theme’s folder in /wp-content/themes/. You should be able to log in now. Restore the theme and plugin folder names. Restore your normal theme and plugins, one at a time. Log out/in after each to test. When the problem recurs, the last activated module is the cause.
You’ll need to rename that module’s folder so you can log in again. Seek advice on fixing the problem through the module’s dedicated support channel where its devs and expert users will be able to help you.
The problem plugin was wp-user-frontend.
I’ve submitted a ticket to wp-user-frontend’s support.