I have found one issue with v21 and that is the sessions getting confused with one another, ie even when the paths were set correct for a new session images would get saved in the output folder of the previous one.
I do think in many ways C1 is over complex especially for what should be a simple thing, images in and images out. It is also incredibly slow to load images in as well ,for example 300 raws and jpegs well over ten minutes on a machine that is gen 8 i7 ,32 gb ram and nvidia1070ti 8 gig on board, this computer can get 70fps with the Toliss airbus in Xplane 11 with all the sliders to the right! C1 is certainly not well optimised.
Having said that C1s output results are nothing short of superb, haven't found anything better and have tried most. It amazes me how much you can squeeze from a raf especially highlight recovery from bright over done skies.