I have found a workaround solution until the Events module integration with Groups can be fixed. Members who are creating an event for a group (who are not the site admin) can use the "Share to context" button on the timeline post for the event (You can do this with a new post. But if you delete the original new post, the shared post will disappear from the events page.) After clicking the button, select to share it to the new event. This will put a copied post with the event banner inside the event page so that all of the attendees can comment and talk. It's not ideal, but it works.