It appears that access to the Steam Community, including forums, user profile pages, and inventories, has been blocked in China. According to Greatfire.org, a site that monitors online censorship in the country, access to steamcommunity.com has actually been 95 percent blocked since December 15.
Steam users in China can still access the Steam store to buy games, and they can still play their games of course. But given that the number of users of the service has skyrocketed thanks to the popularity of games like PUBG, this means that a huge percentage of the overall Steam userbase has been blocked from engaging with the community.
Chinese authorities have a long and well-established history of acting arbitrarily to ensure advantages for Chinese businesses, and this would certainly fit that pattern. Although it remains to be seen if there will be any further crackdown by Chinese authorities against gaming services.