When the Optimize PDF Separations task is used to remove separations, the resulting files may have some errors because of "Missing halftone information".
The Optimize PDF Separations task is used to remove unwanted separations when going to the proof/ plate. In some files, it results in a Normalized PDF that is "Missing halftone information". This happens when separations are removed, resulting in objects that no longer contain printable separations (i.e. become white).