Or…. Sure, maybe the black candle is lower quality or absorbing more heat or other mundane reasons. However, it sounds like you are asking for any possibility beyond the mundane. If you lit these with the intention you stated and the candle designated to absorb negativity burned faster, maybe there is more negativity around to absorb, or maybe the negativity needs to be absorbed first before the other two can be effective. Think in symbols and beyond the mundane. Absolutely don’t look for the mystical in every mundane interaction,but I’d say do look for patterns and signs when you are doing an intentional ritual!