If traders lose more than their initial investment, it is possible the broker offers high leverage and trader choose high leverage let say 1:1000, ideally choose high leverage if open any order will need the smallest margin requirement and could make them open bigger lot size, on another side, it will quickly reduce margin level when the balance is too small and they only eligible to open smallest position size, it possible when face margin call account then end balance become negative or losing more than the initial investment. maybe because price moving fast and brokers face delays in executing orders. so choosing low leverage will be safer than high leverage