same issue here. For testing just to make sure if any of my other plugins or themes are not the cause, I have installed bbPress on a fresh WP install without any other plugins and I get the same error.
I had the same problem. It seems the environment variables used at the function bbp_logout_url inside
bbp-common-functions.php was not working well at http server here or are deprecated. So, I changed the line <$redirect_to = home_url( isset( $_SERVER ) ? $_SERVER : ” );> with this one <$redirect_to = $_SERVER.$_SERVER;>. I do not know if this fixed the problem definitly , because i am testing yet, but the redirect error stoped to occur.
which suggested to comment out lines 938 and 939 of bbp-user-template.php.
Doing that makes the 404 go away. But now I’m being redirected to my S2member login welcome page… which I don’t want. I want forum users who log in to be re-directed to the last forum page they were on. Seems like that’s what bbpress is trying to do, it’s just adding an extra subdomain in the forum url.
Sorry for the bump. Just thought I would add that info in case it helps.