We are having exactly the same issue and it impacts our application and our users. Could Apple expedite the investigation to resolve the issue?

Yes, I have experienced exactly the same since Sun 15th Jun 04:30 (UTC+7) and it significantly impacts our customers. I also raised in this forum. Currently, Apple reports in https://developer.apple.com/system-status/ that App Attest is now having the performance issue. It has been already more than 10 hours that this problem still persists.