GAPFILL: I scored more than the target, so why can't I proceed to the next activity?

This blog post relates to SEQUENCES (assignments based on one or more activities, which can each have a pass mark).

I get a lot of people contacting me about this sort of issue in relation to the gapfill activity: a student has scored more than the target grade, so why won't it let them move on? 

Here are a couple of reasons why this happens...