Yes, it is possible to lose your trading bonus if you experience losses while trading.
However, you never have to refund or repay the bonus, even if it is fully lost.
To summarize:
Can the bonus be lost through trading? → Yes.
Do you need to pay it back? → No.
The bonus is provided solely for trading purposes.
If you lose the bonus through trading activity, it is simply removed—there is no obligation to return anything.