When I go to refund an installment of a recurring gift, I am only given the option to refund from the most recent transaction for that gift. For example if there are 3 installments in a recurring gift, I can't just refund the second installment nor can I refund a portion of all of the installments. When I click on "Refund" next to an installment that is not the most current, the confirmation code for the last transaction is shown and a message that says "You're trying to refund a recurring gift that has multiple payments. This transaction will refund the last such payment".
This is a known, but confusing, limitation with Luminate. A recurring gift is viewed as one "gift" composed of multiple transactions, so when you go to refund part of a recurring gift it's paying attention to the total gift amount, not the amounts of individual installments. So by design, it is not possible to refund a portion of each installment, only to refund a portion of the whole gift, which will always be taken out of the last transaction for that gift.