Every day there is a small chance(proportional to the number of slaves)that slaves will be removed from a guild list. If the number of slaves drops below 6 then there is a small chance that a new slave will be added. If the number of slaves drops below 4 then the guild is guaranteed to gain at least one more slave. To reset the guild slaves, there must be less than 2 slaves and you must restart(save, quit to main menu, and load may work)