SEN0644 STOPPED WORKING (READS ALWAY 0 EVEN IF MODBUS IS OK)

I've bought 6 SEN0644 … I installed them and connected through PC MODBUS DOCTOR …all function well but after some trials, the sensors output always 0 value even if it continues operating with modbus … it seems like the probe has broken … it happaned on all sensors one by one.

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Why???