Just opened a support case for this issue. Noticed on April 13th in the morning that when a build would finish, I never got an email. Always did before. But the build finished and it was pushed to TestFlight.
Created a new iOS app yesterday. No build emails. And no Invite emails to Internal groups regardless of how many times I removed and re-sent the invites.
Clearly it's not working as many people are now posting this issue again. Checked the Apple Status pages but there was nothing for this bug we're experiencing.