There are three main reasons for automatic closing of a trade in MetaTrader terminals:
1. A transaction may be closed if a Stop-Out operation has been triggered on your account.
The Stop-Out operation means that your positions were forcibly closed at the current prices at the time of closing. This occurs due to reaching the acceptable level of losses and the resulting lack of funds for further maintenance of open positions.
Transactions are closed using the Stop-Out procedure when the Equity / Margin ratio reaches 50%.
It is quite easy to control the level of funds (margin level) in the MetaTrader terminal. It is displayed in the "Trading" tab when there are open trades as the "Margin Level" indicator. It is determined by the formula: (Equity / Margin) * 100%
In the account history, a Stopout operation will have a comment like [stopout] or [so].
2. An Expert Advisor or a robot is enabled in your trading terminal.
Expert Advisor/Robot/Autotrading is a certain automation setting, which, when enabled, independently concludes and closes deals in accordance with the specified algorithm.
As a rule, the presence of an enabled Expert Advisor is displayed as a "smiley face" in the upper right corner of the chart. If the smiley face is sad - autotrading is not enabled. If the smiley face is smiling - it means that your EA is allowed to trade, so it will open and close trades on its own.
As a rule, an Expert Advisor leaves marks indicating its activity. In the Account History in the "Comment" column, an Expert Advisor can leave a message that this trade was opened/closed by the Expert Advisor. However, some EAs do not leave marks depending on their internal settings.
It is important to make sure that trades have not been closed by the EA by checking the account history, as well as signs of its presence in the terminal.
3. In case of set profit or loss limits (i.e. Stop-Loss or Take-Profit).
When opening a trade in the MetaTrader terminal, you may be offered to set profit and loss limits. If you set such limits, the trade will be automatically closed when these conditions are reached. Profit and loss limits can be set both when opening trades and in currently open trades.
All situations when trades may be closed without your knowledge are described in the Terms and Conditions.