In my site, I turned off one of the plugins. Now is OK.
I have the same problem
Warning: Cannot modify header information – headers already sent by (output started at /wp-includes/general-template.php:2099) in /wp-includes/class-wp-ajax-response.php on line 129
Warning: Cannot modify header information – headers already sent by (output started at /wp-includes/general-template.php:2099) in /wp-includes/pluggable.php on line 881
