I'm having the same issue. I reported it via Feedback Assistant and got the same 'fix' about removing the tester from the account. The only issue with this fix is they note that the tester is not deleted until the last build they were invited to expires (up to 90 days). I asked if the tester can not be re-invited until after the build expired and they confirmed that was the case. Having to wait 90 days makes this an unacceptable workaround in my opinion. I asked if there was any plan to address but have not received a response yet.