This looks like a major bug, Im trying to Invite team members via the Users and Access tab it says "sending invitation link" but they don't receive any mail. tried 20 different emails.
a major bug while Inviting team members via the Users and Access
Exactly same issue here ! Stuck trying to send app to TestFlight testers ..
The is the link https://appstoreconnect.apple.com/access/users
its broken since yesterday and apple does not seem to care.