As long as you’ve reported to dragon lady you get the chest when it fills up. If you show up late you won’t get them.
My last 2 events my objectives bugged and I couldn’t continue, destroy three grain, couldn’t find the third one.
Fix the control panel, it literally disappeared in front of my eyes lol.
Ofc I afked at the portal lol. Some nice person whispered me that if you leave the area and come back it should fix it. Haven’t tried yet though.
Sometimes your events bug out and you can’t progress, but you can still go around killing mobs for other peoples events that give event progress.