How contributions are created as part of a recurring series is not well-defined by CiviCRM core, it depends on the payment processor.
iATS Payments will create the new contribution in the recurring sequence based on a combination of:
1. the settings in the recurring record and
2. it's best guess of a previous contribution to use as a template (i.e. the most recent contribution in the sequence that has a matching amount).
The code that generates the contributions and payments is here: https://github.com/iATSPayments/com.iatspayments.civicrm/blob/master/api/v3/Job/Iatsrecurringcontributions.php
So either it's not finding the right contribution to use as a template, or in your case, since it's an issue with all recurring contributions, I suspect it's a code issue, worth posting to the iATS extension issue queue, here: