You may have experienced this. You enter a trade and suddenly your spread goes bananas.
There is a certain time you shouldn’t trade, an that is form 23:00 to 00:30 Cyprus time.
Brokers based in Europe do the maintenance during this time, they calculate rebates, dividends, roll over fees, reconcile risk positions and other back office stuff. In order to do this they widen the spread to at least 20 pips in major pairs and they disconnect from liquidity providers. Most of the quote slippage happens during this time, and also most of the “bad” executions and stop loss blow outs.