That's a new one on me. I can't imagine two valves failing at the same time. Not impossible but highly improbable. As per cooltoy, press on the valves (you may need to use a small screwdriver or similar) and see if air leaks out. If you get air out, the valves are good and I have two guesses:
1) The stem on the sensor is too short and you are not getting a good fit with the air chuck because of interference with the wheel.
2) Like Fountainhead says, the Schrader valves are too short and the tip on the chuck is not pressing on the valve.
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