I've noticed this as well, sometimes. Perhaps a bug report is in order, or at least a greater explanation on SE's part about why it doesn't happen. I haven't been able to find any correlation between time and/or crystals and/or ranking. It either happens when you reach the appropriate rank, or it doesn't. My own experiences lead me to believe that the problem happens when you have main plot and class quests available to you; but that is just anecdotal. I haven't really payed attention to it.