A new Change Order to downgrade all purchased resource was placed from the vendor's Control Panel or using the PlaceResourceUpgradeOrder_API method. The order details contain less amount of the resource than are displayed on the subscription's "Resources" tab.
For example, there is a subscription having 10 units of an additionally purchased resource (it is displayed in the "Additional" field). Its owner places a Change Order to downgrade all resource units but the order detail contains less than 10 units. When the order is provisioned, all additional resource amount is downgraded.
This behaviour is acknowledged as an internal software issue #PBA-82880. It affects subscriptions having an unprocessed downgrade Change Order for this resource which was created before a Billing or Renewal Order but cancelled/archived after it. This scenario is described in KB121414: "Ordered (not yet provisioned resources) are included in renewal/billing orders".
It is not possible to correct details of already generated orders. A Credit Memo document can be issued to correct a customer's balance.
Contact your Technical Account Manager or Pooled Technical Associate Team at firstname.lastname@example.org for clarifying the status of the #PBA-82880 or placing a Hotfix Request for it.