In the run up to its total ban on pornography, Tumblr is using "algorithms" to determine if current posts are pornographic at all.
For some reason, the blogging site hopes that people running porn blogs will, after the December 17th ban, continue to use the site, but restrict their postings to the non-pornographic. As such, it isn't just banning or closing blogs that are currently used for porn; instead, it's analyzing each image and marking those it deems to be pornographic as "explicit." The display of explicit content will be suppressed, leaving behind a wasteland of effectively empty porn blogs.
This would be bad enough for Tumblr users if it were being done effectively, but naturally, it isn't. No doubt using the wonderful power of machine learning —a thing companies often do to distance themselves from any responsibility for the actions taken by their algorithms—Tumblr is flagging non-adult content as adult content, and vice versa. Twitter is filling with complaints about the poor job the algorithm is doing.