Metadata being lost/corrupt

Anyone seen this happen before ?

I have a metadata column called Business Area which has a choice column.  Not too many files in the library, less than 100.  We then group by Business Area.

The pic above shows a file that was in a Business Area called Regulation and Assurance - but the file for some reason loses the correct value in the column and pops out in its own 'unknown' business area.  To fix it we have to change the column back to the correct value.  This happens on a few different libraries that are setup like this.