This scenario usually occurs in a Short trade. In a Short trade, you enter with the Bid price and exit with the Ask price. However, candlestick represents Bid price only. When the candlestick (Bid price) touches your Take Profit, the Ask price would still be higher than your Take Profit level, hence your trade is not exited.
The other possibility is your account has hit the Stop Out limit. Read “FullertonMarkets Margin Call and Stop Out Policy” here.