Change path to store ACF JSON files outside the theme directory

site-config.php

/**
 * Update ACF Local JSON save path.
 */
function ti_acf_json_save_point( $path ) {
	// Update save file path.
	$path = WPMU_PLUGIN_DIR . '/acf-json';
	return $path;
}

add_filter(
	'acf/settings/save_json',
	'ti_acf_json_save_point'
);

/**
 * Update ACF Local JSON load path.
 */
function ti_acf_json_load_point( $paths ) {

	// Remove original path (optional).
	unset($paths[0]);

	// Append load path.
	$paths[] = WPMU_PLUGIN_DIR . '/acf-json';

	return $paths;

}

add_filter(
	'acf/settings/load_json',
	'ti_acf_json_load_point'
);