We have been affected by this for the last three months with a long term client who has so far received the invoice emails fine, despite the "delivery issue" notification. In one case a repeat send cleared the issue within QB online, though the client did receive multiple email copies. Another month the repeat send did not clear the issue within QB, though the client again received multiple copies.

While this continues to be unreliable, we currently therefore have to send PDF copy and/or call the client to ensure they have received the email, which as a one-off isn't too bad, but doing it every month not only wastes time but more importantly looks unprofessional. This is NOT a "solution", it is only a workaround while we wait for this to be resolved.