Games : Why are Online parallel quests not clearing?

I'm doing some of the hard quests online, looking for help to clearing them, but for some reason, in the end sometimes they are not appear as cleared, the message of "finished" and "clear" does appear, but, on the results screen, I'm awarded with exp., zeni, everything but the rank, which stays on black and does not give any rank. I've tried with different and the same quests with similar results. I'm always using my custom hero, but obviously I'm doing something wrong, does anybody knows why this happens? has this happened to anyone else?

Thanks for your time.