All our customers who updated to iOS 26 (including beta versions) are experiencing this issue. It also occurs in Apple’s Unity plug-ins, as it is GameKit wrapper. In iOS 18 and earlier versions, GKLocalPlayer.local.authenticateHandler callbacks worked as expected. However, on iOS 26, the issue persists regardless of the Xcode version used.

Feedback "FB20778831" has been submitted. We hope action will be taken swiftly and issues will be solved. This issue is not limited to our applications. It has been confirmed to affect other developers’ products as well, including competing companies, meaning millions of users are currently affected.