The wind at the airport between 4 to 8pm was forecast to be strong crosswind and CX management probably made an early decision to cancel flight during those period. When you see flight departing, it is probably the forecast weather was not as bad and a few flight managed to get out ok. To be honest, it is better to make a decision early and tell passenger that you are going to cancelled flight early before they arrive at the airport, instead of having a few thousands grumpy passenger all at the airport terminal and all trying to ask the ground staff what happen to their flight and cause a chaos.