hysics2D.GetIgnoreCollision not persisting,physics2d.ignorecollisions not persisting

In my game, I'm trying to make it so that you can't hit the same enemy more than once with the same swing of the sword, but you can still hit other enemies.

The sword's collision is represented by a boxcollider2d.

in OnTriggerEnter2D(), I am calling Physics2D.IgnoreCollision(SwordCollider, collision,true) where SwordCollider is the previously saved boxcollider2d of the sword and collision is the Collider2D given by OnTriggerEnter2D(). I can verify with Physics2D.GetIgnoreCollision(SwordCollider, collision) directly after the ignore call that the ignore has been set, but it will still allow further OnTriggerEnter2D() calls to happen (verified with debug.log) and if I check with GetIgnoreCollision() It returns false each time. it seems to be losing the ignore setting, but I'm not doing anything like turning off the collider or gameobject to cause this.

please help!