The pixel breath algorithm uses a cross correlation to find a phase shift compared to the summed signal. In case of a large disturbance in the signal, the cross correlation have an unexpected shape, making it impossible to calculate the phase shift. The pixel breath signal should possibly not be used on this type of data, as it is not stable enough.

This is the example this bug was found in. This was a piece of signal deemed stable. The peak at the start of the pixel impedance is the result of some disturbance. As a result, the cross correlation deflects to a negative value around the center, so no local peak can be determined.