Agent Last Contact information is inaccurate on (at least) build 10.0.653

Last Contact time is out of sync with Last Scan Time.  I assume a Scan includes Contact.  Is this by design?  Previously the Last Contact time was at least once daily, and now it is days behind for machines that are always/constantly online.  All boxes are still showing scanned at least once daily.

I can't be sure when this issue was introduced, because this MEDC instance is updated often.

Thanks!