The login keeps looping. How do I fix it?
Reload from a verified address, allow first-party cookies, and type into the real login field.
Short answer. A login that returns you to the login page usually has a simple cause: a stale page, blocked cookies, or the wrong field. Reload from a verified address, allow first-party cookies, and fill the visible field by hand.
Reload and cookies
Open a fresh copy of the login from a verified address rather than a page that has been sitting open. Tor Browser at Safest still allows first-party cookies, which the session needs, so if you have blocked them for the site the login will loop.
The right field
If your password manager is filling a honeypot decoy, the real field stays empty and the login fails. Fill the visible field by hand. And confirm the captcha address matches your bar, because a clone can loop you deliberately.