I frequently can't claim the rewards from timed quests. I spent just about 10 minutes fighting an Ancient Leshen with no consumables for the "no fire" quest, but when I'd tap "claim", nothing would happen. After fiddling around for a few minutes (playing another fight, opening and closing various menus), I closed and opened the app, only to see that I've no longer "completed" that quest. It's a fun game but it's a frustrating mess that I wouldn't recommend.