Hmmm....I had a preexisting Pop Standard room booked for late September, with dining and park hopper added (we were going whether we got deal or not). After seeing nothing live at midnight, I set my alarm ten minutes before 5 am cst, and checked on my iPad once I got up. I hit "modify", and it gave me a list of options of rooms at Pop (not just saying my current one was unavailable), as though I were making a new reservation. My standard was greyed out as not available, but the "standard pool" was available which is what I went with (after piddling around in POR for awhile, but resisting the temptation of switching over-- just can't justify the extra cost when DH and I are out n about so much in the parks and other resorts-- hah). Next screens took me to reselecting our park hopper and dining plans. It seemed that once I hit "modify" on my existing reservation, it almost cancelled out everything, as though I were rebooking each part again. Took all of 5 minutes.
Honestly I think a lot of it has to do with when you signed on, people's internet connections, people's different devices (laptop, iPads, Chrome, Safari, etc), how many people were on at once, which resorts you were trying to book with how many people/rooms at once, etc. etc. Not so much if you had a preexisting reservation or not.