Auto-Pay drafts only if the remaining available balance in your linked account is more than $10 after Auto-Pay drafts your minimum payment due. Banks tend to pick and choose which transactions they label as the cause of an overdraft and ACH transfers like Auto-Pay are easy targets because they don't process immediately.
Challenge the bank by asking them:
“What was my account balance when the payment was initiated?”
If the bank answers 'you had sufficient funds when the payment was initiated,' then ask them:
“Why was this transaction labeled as the cause of the overdraft if there were sufficient funds available?”