Why are my custom fields missing from the Accounts or Subscriptions export?

Custom fields will only appear in the export related to the Recurly Object they were created under.

For example, if you create Custom Field A under the Recurly Subscriptions object, that fields will only appear in the Subscriptions export. 

If it were created under the Recurly Account object, the field would appear in the Accounts export. 

Therefore, the custom field will only appear in one export, either the Accounts export or the Subscriptions export - depending on which Recurly Object you create it under.