Interesting, I searched CK and it seems like this error happened before
1. Back in 2022, when a bunch of pets temporarily became UC, and
2. End of January 2024, which IIRC is about when NCUCs were released.
Wonder if they're working on the next wave of NCUCs, and that entails botching the entire site for some reason
ETA: 1:40pm NST: aaaand we're back!