Hi,
I don’t know if it is a bug. When you do one adventure’s island scheduled, it desactivate reward for 5 others island in the day.
For example, i do event on Harmony Island at 11:00 am (Today) and i can’t do Tranquil Island and Asura Island. Moreover it desactivate reward for 3 other adventure’s island later in the same day : Forpe, Blue Hole Island and Medeia.
So i agree that a coop event can be done once per day. But if people have a time to play on weekend, he will be able to do only one island among 6 island appeared one or two times per week. These island give reward to player randomnly. With bad luck and only few hour to play, player will despise the game.