TCPDF stopped working after updating yii2


I have an application that was generating pdf files using TCPDF, working well on Yii 2.0.1.

After a composer update which upgraded Yii version to Yii 2.0.11, the generated files are not downloaded, garbage is shown on a web page instead.

I also tried to integrate kartik-v/yii2-mpdf with the same results. If I test to generate the PDF file on PHP outside the Yii application, it works OK.

Any help is welcome

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