Screen time app limit not working

Hello. I have set up a 2 hour screen time on my son's iPhone and at night when he goes to bed, I see that the device has been used a lot more. I can see that a lot of parents have similar issues. It seems that app limit just isn't working. I am sure it is set up properly, I reset the app limit several times, all of the settings are correct. Has anyone found a solution for this matter. Thank you.