First, you don’t need to care about the empty files. They were once for previous versions of the community list of commands which can be found here: GitHub - dtschump/gmic-community: Community contributions to the G'MIC software.
_gui_filter_sources only appears once, and only affects fetching new filter sources, so it’s nothing to do with the image.
I think you will need to enable debug to see just what the thing is doing - or alternatively take apart the entire fx_pahlsson_descreen command by commenting bits of it out and seeing what’s messing up. My first thought is that crop2=0,{original,h},100%,100%,0 should instead be crop2=0,{original,w},100%,100%,0. A clue would be that the distortions appear to fit neatly into a square portion of the image. That’s just for comparison. Now I’m thinking that it’s to do with the FFT on the cyan channel since those artefacts look FFT-ish to me.