Yeah, the progress has to be quite significant, no points are awarded for trivial observations. Thus scores are usually bimodal around 0 and 7. In the linked stats you can see that 1 point for P3/P5 was less common than full score on other problems.
Problem 2 and 5 have a lot of 1s. Sometimes thre is an interesting advance that is easirr than the full solution. Also in problem 6 the only hope for most was to get that 1 point.