CIS 7 - Rating Scans - Missing Files During Scan?

I ran 5 Rating Scans in a row - one right after another without opening any applications nor installing any new software.

Each time CIS 7 identified files as Unknown that obviously were not included in the previous scan(s).

My question is this:

Is this normal for CIS - or is the Scan functionality malfunctioning (missing files during scan)?