Preflight Page Description Errors - Acrobat Pro DC

For some years, my organization has had a customized Preflight profile that checks 3 things: Unicode mapping, embedded fonts, and standard page size (8.5 X 11).  Our sister office out of state recently upgraded to Acrobat Pro DC, but my office has not.  The sister office discovered that our Preflight profile still works as intended in DC, except an additional error message appears on all PDFs, even when no problems are found with the 3 original checks.  The error is "Page Description Errors," and when expanded it also says "A required 'Subtype' entry is missing."

I have been searching for anything to explain the meaning of this error, why it appears when running a profile that didn't include this among its checks, and whether our personnel should be concerned with this error or ignore it -- all to no avail.  I would even like to know if I can disable the check, or at least the error it reports, if I find out it doesn't affect our publications.  I have discovered in Acrobat Pro XI (in my office) that there are checks that would result in this error, but we've never seen the error before in Acrobat Pro 9-11, and the profile has not been changed for those in the other office that have Acrobat Pro DC.

Any answers would be greatly appreciated.