Upon completing a payment using iDEAL the page redirects back to the site automatically but there's a "Return to merchant" button that appears while the donor is redirected. If the donor clicks on that button, they're taken to the Failed Donation page. If the donor lets the redirection go automatically they're correctly taken to the donation receipt page.
In both cases, the payment is correctly completed in Stripe. In GiveWP only the donation that waits for the automatic redirection is recorded as Complete.