Hey Long, thanks
Yes, it is quite possible that this comes from ACF...
I changed it in my code but still get an error - I forgot to mention it in my first post.
Error Message:
Call to undefined function rwmb_get_value()
On line: 1
<?php $favicon = rwmb_get_value( 'favicon', ['object_type' => 'setting'], 'site_option' ) ?>
<?php
add_action('wp_head', function(){
?>
<script type="text/javascript">
var link = document.querySelector("link[rel~='icon']");
if (!link) {
link = document.createElement('link');
link.rel = 'icon';
document.getElementsByTagName('head')[0].appendChild(link);
}
link.href = '<?php echo $favicon; ?>';
</script>
<?php
});