I'm experiencing the exact same issue. My support case ID is 102919115634. The problem first appeared after a failure in our CI/CD pipeline. The failure was caused by a bug in Xcode 26's altool (see: https://github.com/fastlane/fastlane/discussions/29680). It's possible that this was the trigger for the issue.

I have the same issue. Until about a week ago, our testers were able to install beta builds through TestFlight without any problems. Then, all existing builds suddenly showed as expired. New builds are uploaded successfully, pass validation, and appear in TestFlight. Testers also receive push notifications about new builds being available. However, none of the builds can be installed. Every installation attempt fails with the error: "The requested app is not available..." We also tried creating a completely new app with a different Bundle ID, but the issue persists there as well. At this point, I'm waiting for a response from Apple Support.