A package can arrive at the packing bench with a small Data Matrix symbol near a folded seam, scan successfully once, and fail the next time.
The operator may see a sharp-looking pattern, yet the reader is working with tiny cells, changing reflections, and limited room to aim.
Treat the fault as an interaction between the printed code, the reader’s optics, and the way the package is presented. A capable datamatrix reader can handle a wide range of symbols, but it still needs a clear target, suitable focus, and a repeatable scanning method.