While I am not able to provide much in the way of details when large groups of guild members are all penalized around the same time it is because they have been found to have exploited the game terrain, such as going through walls, going underground, or otherwise circumventing the normal mechanics of the game.
The email should have provided the penalty duration, the display in the client is very much off, which our teams are aware of.
If you believe the action is in error, please be sure to submit an appeal.