Adding User to Groups Still Takes Days?

I sent an Invitation to a known MuseScore user last night at 2000 hrs.
This morning at 1000 hrs he had not yet received his invitation activation email.
I re-invited him two more times, once with his user name and again with the email associated with his account.
As of 1200 hrs today, he has not yet received any email from MuseScore, even though each time I got the green confirmation message that he had been re-invited.
Is there a persistent problem with how MuseScore.com adds members to Groups?