1. What kind of wax do you use? Is it suitable for candles that are cast in molds? Is it suitable for standing (pillar) candles? You should read this information in the description of your wax or ask the seller / manufacturer if there is no such information.
2. What is the temperature of pouring the wax into the mold? Is it too low? Or are you overheating the wax? You must follow the recommended temperature for your wax. Try a lower and higher one than you are using and see the result. The temperature in the room where you are making the candle is also important. It shouldn't be hot or cold