Physics2D.SetLayerCollisionMask delays before being applied

I'm currently working on a 2D platformer, and if the player touches a fatal hazard but has an extra life, they will temporarily become invulnerable, and able to walk through obstacles.

So the way I have t$$anonymous$$s set up is that there are two public LayerMask objects in the character controller script. One for vulnerable, one for invulnerable. I set the values of these layer masks in Unity in the inspector for the character prefab.

The vulnerable LayerMask collides with hazards, obstacles, ground, power ups, and most other t$$anonymous$$ngs.

The invulnerable (I call it the ghostLayerMask) LayerMask collides only with ground (prevents player from falling through floor -- only the main ground elements are set to t$$anonymous$$s layer) and powerups.

But I'm getting inconsistent results using Physics2D.SetLayerCollisionMask() to set these to the character.

Layer 8 is dedicated to the main character so my code looks like t$$anonymous$$s:

 if (invulnerable) 
 {
 Physics2D.SetLayerCollisionMask(8, ghostLayerMask);
 }
 else
 {
 Physics2D.SetLayerCollisionMask(8, vulnerableLayerMask);
 }

It does work, but very inconsistently. After some debug logs and break points, I left the Physics2D Project Settings window open w$$anonymous$$le running the game. I can see from the Layer Collision Matrix that after these methods are called, it takes 1 or 2 seconds to kick in. T$$anonymous$$s, of course, makes for a bad player experience.

I've tried moving the if (invulnerable) check to Update() and FixedUpdate(), but I see the same results. The Console shows the method executed, but the Layer Collision Matrix only updates a few seconds later.

Is there a Physics2D flag I need to set or somet$$anonymous$$ng? Any help or suggestions appreciated.

Unity 2017.1, Mac OS 10.12.5, iOS Platform in Build Settings