RSS dont work after upgrade

Hi there

I need assistance please the RSS dont work anymore after install new version of wordpres yesterday This is 1 of the 3 websites that have the problem.
https://www.artofpianoplaying.com
I another article on the forum about two years ago they mention about a double header in the header.php but i dont see it there, however i see it when i look in the browser the source.
Someone please help me with this?

Thanks