Updated yii from the archive and threw back the controllers, models, views from a previously written project. and got this error.
Fatal error: Uncaught yii\\web\\HeadersAlreadySentException: Headers already sent in /home/alex/server/foogine.io/vendor/yiisoft/yii2/web/Response.php on line 414. in /home/alex/server/foogine.io/vendor/yiisoft/yii2/web/Response.php:366 Stack trace: #0 /home/alex/server/foogine.io/vendor/yiisoft/yii2/web/Response.php(339): yii\\web\esponse->sendHeaders() #1 /home/alex/server/foogine.io/vendor/yiisoft/yii2/web/ErrorHandler.php(135): yii\\web\esponse->send() #2 /home/alex/server/foogine.io/vendor/yiisoft/yii2/base/ErrorHandler.php(262): yii\\web\\ErrorHandler->renderException(Object(yii\\base\\ErrorException)) #3 [internal function]: yii\\base\\ErrorHandler->handleFatalError() #4 {main} thrown in /home/alex/server/foogine.io/vendor/yiisoft/yii2/web/Response.php on line 366
Scratched turnip, thought that perhaps the controllers, models and types from the old version somehow in conflict. Put a fresh version of yii decided not to add your script, and to see whether the problem is in the drain condition. Installed it opened a start page and saw the same error.

From this we can conclude that the problem in yii. Googled on this topic, but alas found nothing. The impression that this error emerged recently and little is known. Who faced with similar, explain how you can fix this error? I hope there is a solution.