This is most probably because the strategy provider made a withdrawal from his account.
Copy-trading uses the logic of the Equity-to-Equity model to define the volume of all open trades. When a provider withdraws funds, then the system will automatically recalculate the volume of all open trades based on the new equity.
Initially, the Strategy provider’s equity is 4,000 EUR while the Follower’s equity is 1,000 EUR.
The provider opens a trade of 400,000 units (4 lots) on EURUSD.
This trade will be copied with the following volume:
(Follower’s equity / Strategy Provider’s equity ) * Strategy Provider’s volume
(1,000 / 4,000) * 400,000 = 100,000 (1 lot)
Later on, the Strategy Provider withdraws 2,000 EUR from his account.
This will lead to a decrease in the provider’s equity and hence the volume of the existing open trade must be recalculated to meet the Equity-to-Equity logic.
The new volume for this trade is now:
(1,000 / 2,000) * 400,000 = 200,000 units (2 lots).
As a result, the system will automatically open an additional trade so that total volume on EURUSD is equal to 200,000 units.
Since originally there was a trade of 100,000 units, then a new trade of 100,000 units will be opened to meet the Equity-to-Equity ratio.