Internally, the digital isolation inside the MAX14946 has a refresh pulse only if the input is not toggling. So, two modes: 1) if the input is moving, there is no refresh clock, and 2) if the input is not moving, after 3usec the refresh clocks at 1MHz until the input begins moving again. This refresh clock obviously is not reflected at the output, it is common to both sides of the isolation so it is removed.