Ok, from StuckMic, this thread appeared just one week ago in which a young, otherwise clean person received a denial on his clearance as well. This is what he said:
"I had to do a full security check as well. During the interview the lady asked if i ever went by any other names and i said no. She laughed and said okay now i can tell you why we are here. A creditor filled out paperwork wrong at some point in my life and made my name my First, Last, Last instead of First, Middle, Last. She said that dumb stuff like this happens all the time and always flags for a full interview. We still had to go through the entire processes but everything else was correct."