The wincest tumblr is still working and posting stuff: https://www.tumblr.com/ao3wincest Maybe you could message them and see what they did to keep their working? That's the only suggestion I've got because I don't know how you guys got those to work in the first place!
After doing some searching, this seems like a problem many AO3 feed accounts are having. If the Wincest one is still working, they're lucky - it sounds like Tumblr did something that's making things fail. At this point I don't have any other ideas, and I can't get it to reconnect to Tumblr, which means unfortunately this feed is no longer going to update. I'll keep trying off and on over the next week or so, but if you don't see any additional posts, then it's officially dead.
