Test equipment, like many things in life, has limits on what amounts of (anything) it can measure, as well as the conditions for making these tests accurately. Also, keep in mind that test equipment can fail.
In the above example, the first thing to suspect is that the input level to the test equipment is being exceeded, thus overloading the test equipment. When that happens, the test equipment cannot be relied on to give a correct reading. As an easy experiment, try inserting an attenuator (for example, 6dB) in line between the source product and the test equipment. Then look at the displayed noise level. If the displayed noise level did not change, or if it changed by ANY amount other than the amount of attenuation, it is likely that the test equipment is being overdriven, or has failed.