how likely is it for microchip to “fail”

my cat got out abt a month ago and a cat posted on my local shelters found cat page yesterday looks very similar. i called the shelter abt a different cat before but they assured me they would call if a microchip was detected (and i checked w microchip company that my cat is registered to my current info). could a microchip fail? i adopted him about 9 months ago he’s not even 2 years old so it feels unlikely but idk how they work. ig i can’t attach photos or i would of my cat and shelters found cat pic