It depends on what type of search you are doing really. If you are doing a keyword search you could probably use something as simple as Search Everything https://wordpress.org/plugins/search-everything/
The thing is that you need to tell it where to search and the content needs to be part of the post you want to return as a result, usually in some hidden post meta field. WP and ACF have some limitations, the best that we can do is work around them.
