Originally Posted by kq747

This was definitely true for me recently. Booked BOS-DXB-BKK in Y flex and opted for a 6+hr layover so I could meet a friend for dinner when there was a ~3hr connection available for booking. When I upgraded the entire journey to J with miles, DC became available and I booked it and had no issues. By my reading, I shouldn't have qualified owing to the earlier flight so not sure if the fare class was the trigger. Just seems so random sometimes.