knx_domo:
I had the same problem, the readings changed continuously. I have 3 sensors with their 3 cards JSN-SR04T-2.0. In my case the problem was due to interference in the SR04T card, the solution was to wrap it in plastic and cover it with aluminum foil. Now I have stable readings when the objects are less than 3 meters away. I'm happy with these sensors. (Yo tube el mismo problema, las lecturas cambiaban continuamente. Tengo 3 sensores con sus 3 tarjetas JSN-SR04T-2.0. En mi caso el problema era debido a interferencias en la tarjeta del SR04T, la solución fué envolverla en plastico y cubrirla con papel aluminio. Ahora tengo lecturas estables cuando los objetos estan a menos de 3 metros. Estoy contento con estos sensores.)
I gave up on JSN SR04T v2.0 because the PCB is not waterproof and it has a blind spot of around 20cm. I went for this one instead: Sealed Waterproof ultrasonic/distance small blind sensor arduino Fully Genuine | eBay