Admob clicks get less

Why in Admob clicks sometimes get less? like you see 50 clicks, after refresh it is 45 or something.

It is because they cancel some clicks? Invalid click activity from someone?
I started to see this especially after I added interstitial on app launch on one of my apps.

Invalid clicks and click fraud. You got it. I’m pretty sure Google can track if a user follows threw with a click.