Basil is a bit touchy when it comes to watering so perhaps the plants that die  get a bit more water or have blocked drainage holes. Mint is the opposite and does not like to dry out. Perhaps if you send a photo or describe how the plants die  (yellow leaves? wilting? ) I can make a more accurate diagnosis.  You have me  stumped if you treat all the plants the same and half just die. Keep growing, Marianne Binetti