why I lost strain signals after adjustment successfully

[Junjunabc]

We have a chassis SCXI 1000 and two types of signal conditioners with their corresponding terminal accesories(SCXI 1520/ SCXI 1314T & SCXI 1121/ SCXI 1321) in our laboratory. and I intend to use all these equipment to make strain measurement (Quarter Bridge I). After we connected the strain gauge and its completion resistor into the electrical circuit, at first we can get the strain signal successfully and later something strange happened.

When we try to adjust the SCXI 1520/ SCXI 1314T slot (which contains 8 channels in this slot), we can get the output signal correctly from channel 1#, then we turn the chassis off, and switched the modular plug (with connected NI 9945 and our measurement strain gauge) into channel 2#, we can also get the strain signal successfully from channel 2#. Now, when you turn off the chassis, and switch back the modular  plug into channel 1#, you will find THERE IS NO STRAIN SIGNAL OUTPUT FROM CHANNEL 1#.  And If we change the low pass filter frequency to a new threshould value (from the software setup interface corresponding to channel 1#), and chang it back again, YOU CAN GET THESE STRAIN SIGNAL OUTPUT AGAIN FROM CHANNEL 1#.

We also met the same strange phenomena when we adjust SCXI 1121/ SCXI 1321slot. because you know we cannot set the low pass filter frequency very quickly (for we have to set the jumpers in SCXI 1121). That means we cannot get he strain signal from channel 1 #  in SCXI 1321 again. It pulzzed me many times, so could someone give me some suggestion how to solve this problem and explain the cause for these strange phenomena for me?