Hook AdminInvoicesControlsOutput not executed

Hello, everyone,
can anyone tell me why, in the admin area of WHMCS 8.10, if an invoice is displayed within the url `admin/invoices.php?action=edit&id=XXXX` the "AdminInvoicesControlsOutput" hook is executed, whereas if the same invoice is displayed under `admin/billing/invoices/XXXX` the hook is NOT executed?
Thank you all!