The News Feed and Documents web parts have disappeared seemingly at random from some of our older "classic" Sharepoint team sites. On affected sites, both parts are gone, effectively resulting in a blank site. Top and side navigation remain, but the main content columns are rendered blank.
When I go to the Site Contents of the affected sites, the Documents and Micro Feed web parts are still listed as on the site, even though they do not show up. I have checked all of the permissions and configurable options, and have compared them to unaffected sites, and no differences are apparent.
No edits have been done to any of these sites and no previous versions exist to restore. It has happened at every hierarchy level. For example, some top level sites have lost their web parts, while others haven't. And then some subsites of any given top level site have lost theirs, while other subsites of the same parent site are fine.
It all happened sometime over the weekend, but I don't see any applicable change notifications that apply to this situation.
I can add the web parts back in, but I'd rather figure out the root problem and restore them all, if possible.