Both the App Store and iTunes is currently experiencing a widespread performance issue resulting in missing content from the categories sections and errors when downloading new content.
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Apple’s official status page currently has no mention of the issue aside from a brief Apple Pay support problem earlier today.
Apple’s services last suffered a widespread outage just two weeks ago which prompted an apology on behalf of the company.
Update 11:36 EST: While the outage was very much widespread, the issues seem to be resolved. Force quitting the App Store or iTunes app should result in seeing content again if the fix isn’t automatic.