Once event for multiple targets happens, it doesn't occur anymore

Hello

i am kind of newbie in Vuforia and Unity, but i already have some experience!

I am trying to make reading cubes for kids attractive again

The idea is simple - when combined C,A,T together - the cat appears and meows.

The problem is - it works always only once and i have to move the carton cards really carefully close to each other.

I tried many values for distance, but it works the same.

Could anyone help to improve the "sensitivity" in my code and correct something in the code so that the cat always appears for combination CAT, but not only once.