AutoCAD 2013 :: Attribute Fields Losing Reference With Sheet Sets

I just opened up a project Sheet Set that i haven't worked on in a while, and all of my layout pages have a series of "#" in place of the fields.  For example, the name of my viewport should read "Head Detail", which is the name given to that view in the Sheet Set Manager, but instead reads "##############".  This also happens with my view numbers, callout bubbles, etc.

However, the information in my title block is still intact.  For example, the Project Name, Client Name, Page Number, etc. all read the correct values.

I tried opening the drawings in Reference Manager, but I see no alerts or errors.  I have had this happen before in previous versions going back to at least 2010, but they have always been small projects and I just recreated the views and callouts.  This is a large project however, and redoing this will cost hours, if not days of extra work.

In examining the fields, it seems like the problem fields are those defined by the SheetSetPlaceholder Filed Name, and the Placeholder type is irrelevent; they are all broken.  For other Field Names, for example CurrentSheetNumber, the references still work.