Your guild quest system has several design flaws. It is broken. Please remove it until the following items can be address:
Lack of guild controls:
There are no tools that lets a guild opt in or out of a daily quild quest. Guilds should be allowed to decide if they want to participate in the system or not. They should also be allowed to cancel specific quests WITHOUT their members losing any materials automatically taken (e.g. Stolen and henseforth lost to them) from the member players.
Lack of management tools:
Guild officers cannot see who has or has not completed the quest. Example: I am a member of a 22 person guild. We are stuck on our first quest, because only 16 of the required 18 have completed the quest. Officers cannot see who has completed the quest to ask them if they need assistance. If they don't know who's stuck, how can they help? (Espeicially when they are on different time zones and schedules.)
Gameplay issues
Stealing of resources from players:
Yes, I call this theft. Your quests place big levies on being a memeber of a guild. These resources are automatically culled from the accounts of the players without giving the players an option to do the quest. Even if they had the chance to cancel the quest, (which they don't) the resources are taken ahead of time without refund. (The player quest system does the same.)
Rewards do not equal the effort:
Rewards culled (i.e. taken or stolen) are not compensated for in any fasion. I'm not going to discuss the XP question, as there are a hundred ways to argule the point back anf forth. I'm talking the OTHER rewards you offer for these quests. You are telling players (Most of them under Level 30) to give up massive amounts of resources and expecting them to go away happy with paltry returns. It's the real world equivalent of walking into a Ferrari dealership, taking 500 cars, and telling the salesmen to be happy that you're giving them five Honda Civics and $200 USD.
Now, I'm a level 39 player who has built up my island's economy to the point that I can take a 5K hit to most resources without flinching, however, most of the players are newer and do not have this ability. And while I can donate materials to some of my fellow players to help them out, it does affect my island's economy when I have to start helping a lot of my fellow guildmates.
Until you fix these issues, the only real advice I can offer people is to quit their guilds to avoid this useless feature.