This is something that has never happened to us in the past. Some of the subscription invoice status reads "not approved." We use the PayPal plugin for customer payments. I do not know if their payment has not cleared with PayPal or if I should approve the subscription. I don't want to give away free subscriptions, so I need to know what that means about the payment.
You have such invoice because you enable option 'Manually Approve New Invoices' aMember -> Configuration -> Setup/Configuration -> Advanced Fell free to approve all this invoices. You can disable this option if you do not need this feature.