Slippage can occur at any time, and in all market venues, including equities, bonds, currencies, and futures. Slippage is more likely to occur in the forex market when volatility is high, for example due to news events, or during times when the currency pair is trading outside peak market hours. The significant price movement can be seen in the MT4 screenshot.
Another reason to consider, is the more master has subscribers, the more risk of slippage during periods of high volatility.
The slippage happens in all brokers, MTrading is a low to no slippage broker!