After 30+ days, if a site hasn't been updated and is inactive it will automatically put the media to sleep. This means that the media is being stored until needed. 

Note: the first (4) tiles aren't put to sleep and are still available because these images appear on the site when you do a search in the Site tab. 

How to Wake Up Media

Click the “Wake Up Media” button at the top of the Site Media page to start the wake up. The time to restore the media will vary based on the amount of content. Once finished, the Download Page button will appear as usual.