Was there an international event in Shanghai at that time? If they expected a large number of foreigners in a particular region they would relax the censorship in that particular region. They could even do it per hotel room where hotel rooms booked by foreigners automatically have lesser interference between GFW.
That might be it. I was there every year for about a 15 year period but this may have been around the time of the 2010 Expo. Though I was not in hotels, I was in apartments (ones owned and lived in by Chinese, not foreigners).
