Kick count

I’m 28 weeks and 3 days I started doing kick counts and normally she hits the 10 kicks in less then 15 mins. Today for some reason she’s not very active. I have an anterior placenta so idk if that plays a factor. I was worried so I did kick counts and she did 10 kicks in about 40 mins. That I noticed. Should I not worry since she still made the amount in less then 2 hours??