Why Is That?

Around 10:40 p.m. I was able to grab a 11.00 opp from PPP, however, I was so sleepy and I know I won't be able to write anything right there and then. So I decided to take a quick nap since I know I have six hours to complete the opp. At around 1 a.m. I woke up and refreshed my PPP page and to my surprise the opp that I reserved isn't in the list anymore! Duh! This has happened to me three times already (oh make it four). I dont' know why... was it because my real rank changed (it was before midnite when I reserved it, so you know RR will change after midnite) after I reserve the opp? I have no idea why.. If I wasn't too sleepy, I would have done that and won't be fussy about it. :(