The short answer: Field names cannot be numbers.
The long answer:
I suspect that your call to get_fields() when you have fields with numbers as names is causing a php error.
ACF uses the equivalent of get_post_meta($post_id) a core WP function to get all the meta values. This returns an array of meta_key => meta_value pairs. It then loops through these results using
foreach( $meta as $k => $v ) {
This is a standard way to loop through an array where you need the index and value. This creates sets $k to 1, which is then translated into the varialble $1. In PHP, variables that start with a number are syntax errors.
