I travel to Manila from Vienna with one stop in Urumqi (2,5 hours)

and one stop in Guangzhou (4 hours) leaving China within 24 hours. I´m Czech citizen and EU pass holder. Chinese Embassy in Prague hasn´t responded yet, but Slovak consulate in Beijing and Chinese Embassy in Hungary both confirmed, that I can use free transit visa. I also wrote with other Czech travellers that didn´t need visa on this route, just passed through Urumqi without visa and without problems. Can you please explain us why do we need visa for Urumqi?
Thanks,
Petra