Recently, the guild to which I am a member finally unlocked guild missions. We set a time and date to meet and we would activate the mission. When it was activated, the location we were given was in Southsun Cove on the day of a new content update. This created multiple overflow servers and made getting my group together a significant challenge. In the end, we were unable to do the challenge because of the difficulty in coordinating and grouping.
My suggestion is that when there are overflow servers for the locations that guild events are in, that it excludes that location from the list of possible guild missions. Southsun Cove having many overflows during the events have made Guild Bounties, Guild Rushes, and Guild Missions both extremely difficult/next to impossible.