I've found the majority of my clients who are stuck in processing are those for whom we claimed additional Recovery Rebate Credit money.  You know, the ones who obviously qualified but swore they didn't receive some of their stimulus payment.  

I'm just telling them that because of that they will just have to wait until IRS gets to them.  And no, I won't sit on hold to ask about it.  I also direct them to the Where's My Refund tool on IRS.gov so they can look every morning to see if anything has changed.