Back when Rouge/Flash started, and people kept getting multiple canceled orders and banned... They claimed that the invalid payment info junk was due to a fraud prevention program of sorts.
If you make several 1$ orders, especially in a row, it is likely to trigger the same system and get canceled, because that is a common thing fraudulent theft uses--low dollar orders to see if the card goes through.
They (Sephora) claimed to have fixed this or whatever, but it can still be triggered the same as any other bank/store.
It could also just be a glitch in the system?
I don't know why they'd cancel a few orders that were at least 15$ ish though, that makes no sense. I'd contact them on Facebook to ask about it, because I'm a curious dork who bugs them like that, lol.