On Monday evening, it was confirmed that the reason was due to alleged problems with "child sexual exploitation and abuse" on the platform, which managed to slip through Tumblr's filters.
Tumblr is currently working with Apple to get the app reinstated in the App Store now that the illegal images have been pulled. The same should apply for Apple, but we can't confirm this as no such information exists on the App Store. "A routine audit discovered content on our platform that had not yet been included in the industry database", it explained. Evidently all images uploaded to Tumblr are run against a database, with any images that match being automatically blocked.
Apple's App Store guidelines strictly prohibit apps that share content dealing with child sexual abuse and require them to have content filters that flag those types of material. The content was immediately removed from the platform. That's exactly what happened over the weekend, however, when the microblogging social network app was wiped off the face of Apple's app repository. "As this is an industry-wide problem, we work collaboratively with our industry peers and partners like [the National Center for Missing and Exploited Children] (NCMEC) to actively monitor content uploaded to the platform", a Tumblr spokesperson tells Download.com in a statement.
In 2017, South Korea called on the company to remove pornographic content from its site - a request it initially rebuffed, but later complied to. This led to it being banned for a day in Indonesia over the mature content.
It is wonderful how many parents leave on their Instagram location settings.