There is a 24-hour 'black out' period for UPGRADE site: xyz__upgrade KA Search crawl&index jobs schedule before cutover to Prod site.  During the 24-hour 'black out' period (24-hour before the targeted cutover date), the KA Search crawl&index jobs schedule would be suspended.  As a result, end-users are still able to update and publish new KA contents but the content changes won't be indexed (ie, not searchable) until the cutover is completed and the subsequent KA Search crawl&index jobs are resumed to crawl/index/catch up with the content changes from the past 24-hr 'black out' period.