There was a thread recently by the admin here on twitter about issues going on at AO3. From what I understand -- and I may be confused, here -- is that there were bad actors who were using AO3 as a service and sending CSEM to people with the intention of swatting those they sent the CSEM to. AO3 of course disabled the accounts but apparently there's an issue on AO3 where when they disable accounts they do not automatically hide that account's contents, but moderators have to go through the contents manually for some reason and this may have fucked up their legal liability. Because of this,
if you have anything you have posted on AO3 or have any well-loved bookmarks on AO3, I would recommend downloading them for yourself on your local machine/drives. The great thing about AO3 is that it will generate epubs and other formats for you to keep on your own devices, at least, but I understand that's probably a LOT of bookmarks for some people...
I do not know all the details but the twitter thread is
here. It looks like it has had a lot of updates since I last checked and I don't have time right now to go through all the addendums but the point is -- AO3's code and policies may not have been able to meet its US legal obligations to remove illegal material in a timely manner and that could be a legal issue, so back up your work and favorites in case anything happens to the site.
At this point on the internet if you see something you like you like it's hard to know if it will be on there for much longer so just take a copy anyway. You never know when your personal archive will be necessary.