very few, if any, pump gauges read correctly until you pressurize the pump AND tube/tire by pumping until the VALVE SPRING'S FORCE is overcome, and the Hose has Equalized with the tube/tire pressure.

that little spring in the valve is what's causing the misread problem, not the pump, tire/tube, or gauge.
the tiny load of that tiny spring is a big lb/sq. inch load on the tiny valve seat surface/seal.
and the chuck isn't defeating the spring load completely.... that may be an install issue, or just a funky or worn chuck.

it happens on a lot of pumps, and on both schrader and presta valves.... usually more so on presta...
once the entire assembly is equalized, i read the pressure.
a better bike pump will have a pressure release button valve on it... tires are designed with a safety margin of about 20% over max. pressure, more like 40% on some... a regular stand-alone gauge will instantly show the internal pressure of a tire/tube, and a good one has a pres. release button...