Why is everything in a line? Secondary scanners can sometimes falsely tag luggage as harmful. I know this because my layout is somewhat similar to this.
https://forum.apoglabs.com/uploads/db1788/original/2X/0/0d0d131cda04668986b1b910213e6f459185142f.jpeg
Except, I don’t build Primary Scanners as they are quite unreliable. So, the bags from check-in directly go through the secondary scanners. The rejects then go through the manned scanner. And, some of these rejects actually pass through the manned scanner.
I remember @dallas explaining this somewhere in the forum. 
EDIT: This is the thread: Security Scanners Reliability.
EDIT 2: Okay. I’m wrong about the primary scanners. I thought they could report both false positives and false negatives. My bad. 