The score wouldn’t change but the ranks might change as more and more students complete the mock tests. In simple terms…the next group of students might perform better or worse than your child’s group and therefore your child could be ranked slightly lower or higher. This is why we recommend checking the ranks after each weekend to see if the new wave of students has affected your child’s rank.
In your case you probably checked the results very soon after they were released. Then a bunch of new results must have come in from a different test centre an hour or so later, affecting your child’s ranking.