There is an unprocessed Change (Upgrade or Downgrade) order for some resource. Order can be in New, Waiting for Payment or even Failed status, but the service was not actually provisioned and resource limit did not actually change. On a subscription renewal the fee for the resource ordered were included in (or excluded from in case of resource downgrade) the renewal order generated. With different subscription configuration - the resource fee were included in (or excluded from) the Billing Order.
There is Feature request with ID #PBA-15235 directed to our Engineering Team, it will be included in one of the next PBA versions.
It is required to process/cancel the pending order for the resource, issue a credit/debit memo for the required sum to the customer.