According to a developer update on the Steam Forums, reported on by GamesIndustry.biz, the game is experiencing an issue preventing Chinese players from access the whole game. The issue is prompting a hold on preorder sales and standard sales, as well as a delay of the game's release.
"There is a specific issue with the Gears 5 release in China preventing people from accessing the complete game.
Unfortunately, this issue means we have to suspend future sales and pre-orders, as well as the games release, in China at this time.
We are investigating and will provide an update once we have more information. We appreciate your understanding."
The entire situation is confusing. The developers didn't actually say what the issue was, whether it's technical or a commercial problem. It's also worth noting that Steam isn't even officially available in China. Steam users in the country have to use a VPN service to access the storefront.
Stay tuned as the story develops.