Set the condition to "Trigger Once" or use "On Start of Layout" for example. If you having given condition that remain unchanged it is more likely the action will continue to execute creating object.
For example the condition comparing player position:
"is player.X < 200?"---> "create enemy at x = 100, y = 300"
See the statement will keep creating enemy as long as player x position less than 200. In order to make the action executes once, a "Trigger Once" should be added under same condition. Try to experiment by putting "Trigger Once" before or after comparing player position because the result will be different.