the further away you are in your commute in the RER A the worse it is. the segments handled by SNCF (beyond nanterre) are a real pain where they left me stranded when they broke down and they do that more often than you would like. bus, uber, etc no longer work at that moment because well all the passengers flock to them and they don't have the capacity. I happened so often that ended moving to the center of paris just to avoid it.