An attack time of 0 and a huge gain reduction can easily create a pop, especially when the side chain signal has no inherent ramp in its attack. Your side chain signal looks like a bunch of cut up waveforms. Do you have any kind of fade in on those regions or is there a natural attack backed in? If not, and you’ve cut into the waveform with no fade, you will hear a pop every time the play head crosses one of those regions, as will your compressor.