I am experiencing a similar issue but have not had any issues with response times. My app was approved for unlisted distribution and reflects the update in the Pricing and Availability section. When I submit the app for approval, I continue to get a 3.2 rejection - recommending "Custom app distribution" via Apple Business Manager or Apple School Manager. Since this is a new distribution method and based on the responses, I'm not sure if the review team is aware of this update. Different situation but same fundamental problem - I will provide an update if I am able to find a way out of this loop.