Shortcode not working with WordPress updated

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Try removing the brackets and adding the full url:

$url="http://theurl.com";

And for clarity, it’s best to use different names for the tag and function name:

add_shortcode('aggrenda', 'aggrenda_func');
function aggrenda_func() {

    $url="http://theurl.com";

    $response = wp_remote_get( $url );

    echo($response);
}