[Solved] PHP Warning: session_start(): Cannot start session when headers already sent
My logs are filled with this warning:
PHP Warning: session_start(): Cannot start session when headers already sent in /wp-content/plugins/wpforo/wpf-includes/class-notices.php on line 16
I have disabled all plugins except:
wpForo - Blog Cross Posting
And the error still occurs. I can reproduce the error by clicking the wpForo Delete All Caches button.
This error says that wpForo doesn't have any PHP error. Your output is affected by other plugin error and it generates " headers already sent " NOTICE in wpForo functions. It'll generates such notices in all plugins who have session functions. So please find the plugin who generates errors or outputs in header. Deactivate those one by one and check, once the wpForo Notice is gone then the problem is fixed and you found the problem maker plugin.
This error also can be from functions.php of your theme.
Another explanation: https://wordpress.org/support/topic/php-warning-in-cron-daemon/#post-12238846