Game freezes for several seconds very often.

Fairly often, the game will freeze for several seconds. Alt/Cmd-tabbing to a different application seems to cause the game to unfreeze most of the time, but not always. It appears as if the problem is server-side, because the game stops processing events during freezes, however, the freeze also prevents the controls from doing anything and the graphics do not update. I do not know what causes the bug and therefore can not provide you with steps to reproduce it.