I’m experiencing the same issue. Build 1.0 (2) shows “Testing” in my external group, and a tester successfully installed it through a public link. However, all five email-invited testers show “No Builds Available,” and none received an invitation email. Recreating the external group, adding the build first, and re-adding the testers hasn’t resolved it. I’ve also opened a case with Apple Developer Support. For those whose invitations started working again, did you need to resend them or remove and re-add the testers, or did they become available automatically?