Subway commuters in some of China’s biggest cities had just begun to embrace a key tenet of escalator etiquette—standing to one side to let others pass. Now, officials have another message. Never mind.

In a recent spate of newspaper articles, commentaries and social-media posts, elevator experts have warned the practice represents a danger to public safety. That’s because of the uneven wear to escalators caused by so many people standing on the right side, which increases the chances of breakdowns. Besides, they say, escalators...