I was ahead while Apple Watch competition "tallying" but I lost. Why?

Hi there,

I am hoping someone might be able to clear up an issue with Apple Watch competitions.

I was in a 7-day challenge with a friend. I was five points ahead after midnight on the last day, but the other person ended up winning the challenge.

At midnight the Fitness app said it was "tallying" the points.

When I woke up at 5.10am my iPhone said I was on 3381 points and my friend was on 3375:

But their watch at 6.51am the day after the competition ended put them ahead and awarded them the win:

How is this possible?