I\'m using Vuforia and unity for my AR App. which has more than 2 models/image targets. To zoom in and out I used Lean Touch. But the problem is both will get zoom on pinching .
Your method doing the scaling, add :
if(this.gameObject.activeSelf == false){ return; } // Scaling process
So if you run the code on all objects, only the active ones will be affected. Considering you deactivate the object on lost tracking.