Hi there,
The ordering of custom fields is on an internal id, which is why it looks consistent but arbitrary to you. Currently, there is no way to re-order them in the system.
The proper way to get all your custom fields for a candidate is to call this endpoint: `candidates/{id}/custom_fields?per_page=100`. This will give you up to 100 custom field values on the item. The `_embedded` snippet on the other endpoints is just meant as a preview.