Why does my son see different usage times than I do in Family Link

I use Google Family Link to supervise and limit my son's screen time. I see that he and I see different times in the Family Link app. This is what I see:

and this is what he sees:
 
Google Translated Image(original image)

So at the same time, I see he's used 1hr and 38min, while he sees 1hr and 24min. Considering a limit of 1hr and 30min, we disagree on whether or not he's over his limit. Why is there this discrepancy? How can I fix it?