I'm pretty sure someone at ISS or the MSC isn't my buddy. I had a "rank" of 4, then with no notice, or any other changes, it changed back to 2. I didn't miss any shops. Several weeks ago I asked for a shop to be moved up two days because I was going to be there earlier than I thought when I originally scheduled it. She said no problem, and she changed the date.
Dino, the QT shops don't really work that way. Each shop happens during a 4 day span, and you pick a day that you're going to do it. They actually can't reschedule it outside of that 4 day span. Rescheduling isn't even on option that they give you.
And their ranking system is VERY unforgiving. I mostly don't do anything on ISS except restaurant and C-store shops. The other shops they offer have too many downsides to risk losing more points. I do the QT shops because I like their coffee bar dispensers..