Crack in crawl space

A crack which is "no problem" should not be changing visibly in a short period of time. It is, I suppose, possible that it seemed smaller to you earlier and with the inspector's comment you more or less ignored it, and now that it is closer to the move-in date it is looking more worrisome, but assuming that you know what you are talking about and it really has changed, something is going on that is not good. Vertical cracks are usually due to movement of the footing (settling), and this could be caused by unusual water conditions or unusual drying out. But footings should not settle this fast. That much movement in a month would be disastrous in its implications, or possibly the area had an earthquake in the past month that you didn't hear about.