In the streamer versions 3.3 or lower, it may happen that the impedance on measuring electrodes jumps between very low values and NC. Please always make sure to have the most updated version! You can download it from our website.
Make sure to look at the signals on problematic electrodes and confirm the signal seems good. To do this, you need to turn off impedance measurement, as impedance check introduces noise to the data.
If the EEG signal is flat and the electrode is unresponsive, it could be that the electrode itself is malfunctioning. In this case, please contact us for further steps - support@mbraintrain.com