The WWDC video Automatic Strong Passwords and Security Code AutoFill (https://developer.apple.com/videos/play/wwdc2018/204/) demonstrates Suggest Username, by labeling the textContentType of a UITextField with .username.
I've tried this in practice, even in the most basic sample application (2 UITextFields, one with the textContentType as .username, the second with the textContentType as .newPassword), with both Associated Domains and AutoFill Credential Provider setup correctly.
I can confirm my App ID, associated domains, entitlements/capabilities, etc. are setup correctly because AutoFill Suggest Strong Password is working as expected, however, Suggest Username is NOT working as in the video. I do have an iCloud Keychain full of usernames, most of which are the same, so there is data to read from to suggest a username to use.
I'm on iOS 12.0 (16A5339e) and have tried building from Xcode 10.0 beta 4 and Xcode 10.0 beta 5 without success.
Has anyone gotten Suggest Username working? If so, any advice?