The opposite of "more malfunctioning" is "less malfunctioning." When something malfunctions, it means that it isn't working properly. The degree to which it malfunctions can vary. If something is "more malfunctioning," it means that it's malfunctioning to a greater degree than before, or compared to something else. The antonym, "less malfunctioning," would mean that the object is malfunctioning to a lesser degree, or not at all. If something is "less malfunctioning," it may still have some issues, but they are not as severe or frequent. Ultimately, the goal is for something to work as intended without malfunctioning at all.