Were you using this command?
fx_pahlsson_descreen : -skip $*
-pahlsson_descreen
fx_pahlsson_descreen_preview :
-gui_split_preview "-fx_pahlsson_descreen 0",$-1
pahlsson_descreen :
-repeat $! -l[$>] -split_opacity -l[0] -to_rgb
-rgb2cmyk
-split c
-name[-4] C
-pahlsson_descreen_channel[-4]
-name[-3] M
-pahlsson_descreen_channel[-3]
-name[-2] Y
-pahlsson_descreen_channel[-2]
-name[-1] K
-pahlsson_descreen_channel[-1]
-append c
-cmyk2rgb
-endl -a c -endl -done
pahlsson_descreen_channel :
basename={0,b}
-name[0] original
crop1=0,0,{original,w-1},{original,h-1},0
crop2=0,{original,h},100%,100%,0
-float2fft8[original]
-name[original] fft
-i [fft]
-name[-2] real
-name[-1] imaginary
-crop[real] $crop1
-crop[imaginary] $crop2
-i [real]
-name[-1] mask
-dog[mask] 0.5%,0.8%
-normalize[mask] 0,255
-threshold[mask] 64
-normalize[mask] 0,255
-negate[mask]
-ellipse[mask] 50%,50%,7%,7%,255,255,255,255
-i [mask]
-name[-1] blurmask
-blur[blurmask] 1.6%
-normalize[blurmask] 0,255
-mul[mask,blurmask]
-div[mask] 256
-mul[mask,real]
-div[real] 256
-append[real] [imaginary],y
-name[real] fft
-remove[imaginary]
-fft82float[fft]
You can check by going into the G’MIC settings menu and going to the ‘Other’ tab where you’ll be able to set the ‘output messages’ setting to something that will tell you the command and the parameters you used.
IMO that looks like a memory error or something due to the sharp boundary and the fact that it’s affected a portion of the blue channel only.