Since Guild quests apparently calculate the number of members that need to complete personal quests, to allow awarding of the guild bonus, on logins in the previous 2 days (taken from forum posts people have made regarding other Guild Quest bugs)... if a member leaves or goes long term inactive after a new guild quest starts it can never be finished as new members do not get to see the current quest and only get the next one once the current quest is completed.
This seems a horrible piece of logic that obviously will lead to deadlock (Assuming the above information is indeed correct).
People swapping guilds have a 24 hour delay and sure some sort of delay on new members will help stop duplicate accounts being made just to complete quests makes some sense (even if it just highlights the stupidity of the logic behind completion quotas) but to allow one of the few reasons to come back and play daily to get locked out is annoying.
Personally i found the plethora of quests to do after the last update was the most fun I've had with the game in months.. how about giving us weekly quests with a dozen minor goals and rewards just to keep the interest up and give a reason to pop in and do stuff beyond building wells and corn.