Yeah, I've been waiting them to fix this for the past 3 months.. I've tried all suggested workarounds and Apple's support doesn't give any help either. Seems like there's over 2k following this thread so I assume many people are experiencing this issue. Only solution for me is to publish our test builds to external testing.

I sent feedback 4 months ago. I got one reply but that didn't help at all, and I've sent multiple follow-up emails with no response from Apple. I bet this isn't going to get fixed anytime soon.

The suggested workaround didn't even work for us. We've had builds that had expired, and we still couldn't add new testers into it. So I don't even recommend to try their "workaround" as it is waste of time.