PHP enable error

On the homepage of https://online-radio.hu, PHP code has been embedded for years, but recently its execution stopped working on its own.

For example: I created the shortcode [the_ad id=”2740″] with the following content:

<?php
echo "Hello World";
?>

I enabled the “PHP enable” option.

I inserted the above shortcode on the homepage.

Result: In the page source, the full PHP code is displayed:

<?php
echo "Hello World";
?>

But nothing from the above code appears on the homepage itself. (However, if I save plain “text” content, it does appear.)

In the page source view, the PHP code is shown with both opening and closing tags, but it is not rendered on the website.

What could be the cause of this error? It worked fine for years.

The page I need help with: [log in to see the link]