Is it possible for an ATM or one-time debit card transaction to incur an Overdraft Fee on my business account even though it was authorized against sufficient available funds?

Yes, these transactions will be subject to an overdraft fee even when there were sufficient available funds in your account at the time of authorization, but insufficient available funds when the debit card transaction posts to your account, due to other intervening activity occurring in your account. For this reason, you should always ensure there are sufficient available funds in your account to cover all transactions whenever they will post to your account in order to avoid such fees.