Why did my meringue deflate and go soft?
How long did you cook it for?  If it did not form a good crust in the oven it would deflate.  If you used 140 on fan forced oven it could be too hot, which would rise and brown the outsides without forming a crisp crust.    

Usually the rule is to turn the oven off and let it cool completely before removing from the oven, but without the recipe or knowing if there was an intention of "softness", its hard to give specifics.