I am not sure why you are not using the WordPress plugin_dir_url() and instead you created your own helpers_get_dir(), but your function does not account for symlinks. I fixed your plugin for my WP site by replacing $this->settings[‘dir’] with plugin_dir_url(__FILE__) in your acf.php file.
Also you should not use constants like WP_PLUGIN_DIR and WP_CONTENT_DIR in your plugin. These are there only for testing and should not be use on production plugins/themes.
You should look into updating your plugin to use WP core functionally…