Feed not displaying custom attribute values

I am trying to create a feed for Facebook Catalog, with some custom attribute mapping. I can see in the logs that the custom attributes pull through on the configuration:

[13] => Array
                                (
                                    [rowCount] => 13
                                    [attribute] => status
                                    [prefix] => 
                                    [mapfrom] => custom_attributes__stock_status
                                    [suffix] => 
                                )

                            [14] => Array
                                (
                                    [rowCount] => 14
                                    [attribute] => lty_price
                                    [prefix] => 
                                    [mapfrom] => custom_attributes__lty_regular_price
                                    [suffix] => 
                                )

                        )

However in the Feed these are not present at all (not even blank values, the nodes are just not present in the XML.

To test what the issue is, I checked using the Admin Columns plugin to be able to view _lty_regular_price within a product table on Woocommerce, and it indeed pulls through (in this case it is an integer).

I planned to upgrade to Elite today for some advanced features but this is blocking us currently. Please assist.