Не очевидная проблема с простым решением. [RuntimeException] Could not start session because headers have already been sent.
На одном из проектов стала возникать ошибка со следующим содержимым [RuntimeException] Could not start session because headers have already been sent. "/var/www/html/file_test.php":1. (0)
/var/www/html/bitrix/modules/main/lib/session/session.php:144
#0: Bitrix\Main\Session\Session->start()
/var/www/html/bitrix/modules/main/lib/session/kernelsessionproxy.php:47
#1: Bitrix\Main\Session\KernelSessionProxy->start()
/var/www/html/bitrix/modules/main/include.php:168
#2: require_once(string)
/var/www/html/bitrix/modules/main/include/prolog_before...