British passport holders now only receiving 90 day entry visas with a 30 day restriction

Since the middle of June, British passport holders have only been receiving 90 day entry visas, with a 30 day maximum stay restriction once they land in China.

Would you happen to know why this is, as for the past few years, British passport holders have always received 24 month entry visas, with a 90 day maximum stay permitted per trip.