How did I get pregnant on Nexplanon?

I'm 21. I got Nexplanon 2 years ago at age 19. It will be three years come March.

I've had a steady, serious relationship and boyfriend the whole time, now fiance.

We are both clean and healthy. We don't use anything other than my birth control.

I just took a pregnancy test, well 9 of them, digital and normal, and all came back positive.

How did this even happen? Nexplanon is over 99% effective. And this hasn't happened to us in the past 2.5 years...