Your candle may be standing on a slightly sloping surface. If so, turn the candle gently.
Your candle may also be in a draught. In this case, turn the candle or place it gently in a less exposed area.
The surface of your candle must always remain even to avoid the formation of holes that could drown the wicks. We therefore recommend that you do not put out your candle until the wax has liquefied completely.