I am familiar with the contents of the Summary emails. I received more information from our users and it appears that following the update, summary emails are being delivered every day to all users, not just users who have new items in the discussions. Something has changed or gone wrong since applying the update. Most of these users have no new content but continue to get new daily summaries.
Prior to the update you only got summary emails for new messages that were posted that day/previous day. If no messages were posted, you did not receive a summary email, which is the expected behavior.