MetaTrader charts are created using the bid price. Closing of buy orders are activated by the bid price so you may see the chart line hitting the SL (Stop Loss).
On the other hand, closing of sell orders are activated by the ask price, which you will need to enable manually. For this reason, stop losses of sell orders may activate on prices not visible on the chart.
The ASK LINE can be enabled by:
RIGHT-CLICKING on the chart.
Click on COMMON.
Click on SHOW ASK LINE.