The large loan payment was applied as a principal-only payment, which does not move the next payment due date on the loan.  When the payment was reversed using the "95" reverse loan payment code, the due date was backed up and made the loan delinquent.  That evening, the Auto Funds Transfer system tried to satisfy the delinquency on the loan because the delinquency control flag was turned on in the AFT record.

 

Whenever you reverse a loan payment, make sure to review the loan due date before and after the adjustment.  Use the Account Information Update maintenance screen to adjust the due date if it is incorrect.