It's more like TSA doesn't have sufficient evidence to prove we're a terrorist at a given time.

We're still guilty of course. There's just not enough to make it stick.

OP: make sure the screener has clean gloves on and they use a clean square for the machine. The screeners have always swabbed their gloves after a patdown and bag check. Your results could be tainted by the last person's (or persons') results.

They have to change their gloves if you ask. Even if they said "I just changed them" make them do it again if you didn't see it (or even if you did ). Doing so at least lowers the risk of getting hassled in their dragnet.