I was dealing with the same problem recently and found out this was because of not loading WP ‘dashicons’ font in frontend. Is it supposed to load by default?
Anyway, you can try this:
add_action( 'wp_enqueue_scripts', 'load_dashicons_front_end' );
function load_dashicons_front_end() {
wp_enqueue_style( 'dashicons' );
}
It would be nicer if acf would load such icons from it’s css as inline svg for example.
