I am also getting drastic changes in exposure, not really flicker but huge steps. I am not sure how to work around this, so far I have not found a software able to deal with it. I was tring with LRT timelapse (free version) and setting the 'Holy Grail' keyframes manually (I wouldn't mind paying for the full version but first I want to know if it is actually able to deal with those exposure jumps...) but so far nothing really works out, I have a shoot planned for next week and have this sunset timelapse in my mind, I really hope I can find some workflow with good enough results until then...