This can be done directly from the webinterface. Just go to Plugins -> Plugin Editor -> select the Plugin SyntaxHighlighter Evolved -> add the snippet to the end
/**
* Filter to fix issue with & in SyntaxHighlighter Evolved plugin.
*
* @param string $code Code to format.
* @param array $atts Attributes.
* @param string $tag Tag.
*
* @return string
*/
function kagg_syntaxhighlighter_precode( $code, $atts, $tag ) {
if ( 'code' === $tag ) {
$code = wp_specialchars_decode( $code );
}
return $code;
}
add_filter( 'syntaxhighlighter_precode', 'kagg_syntaxhighlighter_precode', 10, 3 );
Sumber: https://nocin.eu/wordpress-syntaxhighlighter-ampersand-character/