I have had this mysterious error before and I never knew where it came from or how to solve it. Sometimes it was there, sometimes not. And I was very scared, because if you don’t know where it comes from and suddenly it occurs in production, what then…?
Now I spent a lot of time in investigating this, and I think I found the explanation.
I was setting up a new apex environment and the behaviour was that accessing the login page via https is ok, while accessing it via http gives the error ERR_TOO_MANY_REDIRECTS.