Loans: change due date fails on existing loans (sample data only)

1. Log into folio-snapshot using diku admin
2. Navigate to user with pre-existing open loans (I use Velva Brakus or Penelope Feil)
3. Open the Change due date modal for the loan (loan details, or user's open loans)
4. Enter new due date and click Save & close

Expected Behavior: the due date changes and displays properly

Observed Behavior: The change due date is not available for the item. An alert is given and the due date does not change.

Notes: Change due date succeeds for newly-created loans on folio-snapshot, but not ones that are included as part of the daily data refresh. Linking to UIU-1012, another bug specifically for those existing loans.