Hmm. Usually this error should indicate that the server temporarily blocked your ip. Due to too many requests.
I sometimes get this error. But since I can immediatly open itch in a second tab of the browser, I have doubts that this is a real 429 situation, as in such a situation the block should be longer than a second.
People seem to be getting this error, when the itch app is running in the background and it tries to update games. I am not running the itch app though.
(If your redirecting would be blocked, it would happen every time and probably with a different message)