Spending whole day to figure out the solution of this issue, congrats to @korobochkin for solving this problem.
Since I’s with WordPress 4.1 and seems it’s have mature multiple sites support, when greping keywords , only these popup, none in the wp-signup.php files.
grep wp_signup_location * -r
wp-admin/includes/ms.php: $sign_up_url = apply_filters( 'wp_signup_location', network_site_url( 'wp-signup.php' ) );
wp-includes/canonical.php: $redirect_url = apply_filters( 'wp_signup_location', network_site_url( 'wp-signup.php' ) );
wp-login.php: wp_redirect( apply_filters( 'wp_signup_location', network_site_url( 'wp-signup.php' ) ) );
Can you put your code for wp-signup.php page-activate.php at https://gist.github.com/ and give a link here?
