Sometimes while logging in via a learner portal on a sandbox environment, the redirects will end up landing the learner on the LMS dashboard, e.g. http://gtx.sandbox.edx.org/dashboard?next=undefined.
It's been proposed that this can happen when working in multiple sandbox environments simultaneously, but we've also heard reports of this occurring on calls with partners, who presumably have only used one sandbox. Since the `?next` query param is probably a JS failure to append a redirect back to the learner portal while sending the user to the `login` URL, it seems like this may be an opportunity for improvement of our default sandbox environment configurations.
UPDATE: We aren't finding this particularly easily replicable/actionable, so we're going to mark that the next step we're not acting on right now is to update the frontend authentication code (which platform folks outside our team wrote) could be updated to the latest versions/means of pulling in as a way of addressing this. As of this writing we're on v5 of @edx/fronend-auth, so if it's been updated in the interim then that's great.