Tumblr's disappearance from Apple's App Store finally has an official reason: what was first simply described as "an issue" was, in fact, child pornography that slipped through the filters — enough of it to make the app vanish. This is not the first time Tumblr runs into pornography-related problems — most likely not the last time, either.
https://www.notebookcheck.net/Tumblr-kicked-out-from-the-App-Store-due-to-child-pornography.365731.0.html