Why has my position closed automatically without stop loss/take profit set up?
Because of the margin call
A margin call is when you get some positions forcefully closed because of the lack of margin. BullRush has a margin call level of 50% and it closes your biggest positions first.
Here are some information about drawdowns which is similar to a margin call
https://faq.bullrush.com/how-do-you-calculate-daily-drawdown