Earlier this month, Tumblr announced that it would no longer allow porn on its platform. Starting Monday, images, GIFs, and videos flagged by Tumblr’s so far flawed NSFW-detection algorithm are now being hidden from public view—and out of the grasp of archivists bent on preserving a storied niche in web history.

Since the announcement, archivists on Tumblr led by a digital preservationist collective called Archive Team have been racing to preserve adult content from Tumblr. It put them under an unprecedented time-crunch, as the platform only gave two weeks’ notice before the adult content started being buried (for comparison, other platforms like GeoCities have given months of notice before deleting or hiding content.)

In the final days leading up to Monday’s deadline, some archivists reported on social media that they were getting IP banned by Tumblr, which kept them from doing their work. An IP ban involves blocking a user based on their IP address, so that no one on that network can access the platform.

Archive Team coordinator Jason Scott reported on Twitter that swaths of Archive Team’s archivists were IP-blocked from accessing the Tumblr API over the weekend. Motherboard reached out to a volunteer contributing to Archive Team’s work, who said that they were IP banned.

Motherboard has been unable to confirm whether the IP bans were automatically triggered because archivists were downloading large amounts of data, or whether they were specifically targeted at archivists to prevent the effort. Tumblr did not respond to multiple requests for comment from Motherboard.

Tumblr’s adult content ban means that the platform will move adult content to be viewable only to the person who posted it—essentially erasing it from view. Once any content on the web is behind privacy or age-restriction walls, it’s typically beyond an archivist’s reach, as the tools most commonly used to mass-mirror or download content can only save what’s in full public view. In Tumblr’s case, archivists can’t save what they can’t access, and starting Monday, that includes all adult content.

Still, archivists have been able to save at least some of Tumblr. According to a real-time tracker for Archive Team’s Tumblr Warrior project, archivists have preserved more than 320,000 Tumblrs from the site, totalling more than 46 terabytes of data.

Though we don’t know for sure why Tumblr is banning archivists, some people Motherboard spoke to have theories: Ernie Smith, a technology journalist who ran his website ShortFormBlog on Tumblr for four years (and regularly contributes to Motherboard), told me that he suspects it’s a matter of tons of people taxing the Tumblr servers at once.

“Archival activity functions not all that dissimilar to a DDOS attack, in that both involve a whole lot of server polling all at once,” he told me in a Twitter message. If this is the case, giving users two weeks’ notice to panic-download the data surely didn’t help the situation.

One archivist who Motherboard spoke to, meanwhile, believes that it was targeted because some archivists were banned but others weren’t.

Being blocked from saving content in bulk is another blow to the content creators Tumblr was built on. An estimated one-quarter of Tumblr users consumed adult content on the platform.

Tumblr’s decision to effectively ban adult content has led to the erasure of stories, history, and communities of often marginalized people who made homes on Tumblr’s platform over the years. Archiving is a way to preserve that history.

One user, who goes by “Deramin,” has been collecting and documenting queer pride flags that have been created and uploaded to Tumblr. Since Tumblr has been relying on algorithms to flag content as being adult in nature, Deramin said on Twitter that at least one of these flag designs—just a few bars of colors—was marked as NSFW.

“Tumblr's about to torch queer history and there's nothing I can do to save it because of content filters,” Deramin wrote in a tweet. “These are not harmless policies. These are not policies that protect children. These are policies that silence queer people and literally destroy our history.”

Deramin told me in a Twitter message that her biggest concern with archiving is not being able to save the context alongside the content. “I can't save any information about the creators or the flag meanings beyond what I wrote down months ago, and no one else will be able to see the primary source for themselves.” If those creators are kicked off Tumblr, and their content put behind a wall, it could be very difficult to ever contact them again.