functions.php

<?php

function my_acf_save_post_searchwp( $post_id ) {
	// re-index the post
	SWP()->purge_post( absint( $post_id ) );
	SWP()->trigger_index();
	// For some reason the above doesn't work unless there is some sort of output below it??
	// The js can be any arbitrary even an alert, which causes an error with acf's redirect function
	// but still updates the searchwp index
	// Without the code below, the post is purged - i.e. the old meta is not found, but the new meta
	// can't be found either
	?>
		<script>
		if (document.referrer != "") {
		   location.href = document.referrer; 
		}
		</script>
	<?php
}

add_action( 'acf/save_post', 'my_acf_save_post_searchwp', 9999 );