Sign-in with Apple not working

Recently my sign-in with apple started working across all of my devices (mac, ipad, iphone, in-browser). The sign-in dialog appears, I hit ‘continue’, asked for a biometric authentication, and then receive a “sign up not completed” error. This is true whether or not I already have an account with the app.

In settings, when I try to see my accounts with different apps (Settings -> [Apple ID] -> [Password & Security] -> [Apps using Apple ID]) i get a “cannot connect to icloud” error. Other icloud features work (e.g. device backup).

I’ve tried signing out of my devices and signing back in. No help.

Any ideas?