Products with the certified gluten-free label must test below 10 ppm and pass a facility screening on a yearly basis to retain the certification. It's unlikely Nima would detect gluten in a certified gluten-free item.
We have done internal testing on several certified gluten-free foods and results have always been a smile.
If a certified gluten-free item tested with Nima results in a gluten-found, we recommend re-testing. If the result is a smile, Nima may have detected a very low level of gluten which might be within the acceptable parameters. If the result is a second gluten-found, we recommend reaching out to the manufacturer.