The x-ray machines often have a problem with imaging of a relatively dense collection of coins packed in a compact holder that can be as thin as a thin, transparent plastic bag or cloth mesh bag. The operators then make up reasons about why such opaque elements must be examined physically rather than just acknowledging the facts about the x-ray machines' and operators capability limitations.

Much the same can go for a dense collection of some printed material too. I used to also find that a bag full of metal minis would drive the screeners crazy too.

The issue of the sort covered by the OP is less a sign of incompetence than a sign of the lying and/or intellectually lazy nature of too many screeners dealing with passengers.