Chinese people know their country’s internet is different. There is no Google, YouTube, Facebook or Twitter. They use euphemisms online to communicate the things they are not supposed to mention. When their posts and accounts are censored, they accept it with resignation.

They live in a parallel online universe. They know it and even joke about it.

Now they are discovering that, beneath a facade bustling with short videos, livestreaming and e-commerce, their internet — and collective online memory — is disappearing in chunks.

A post on WeChat on May 22 that was widely shared reported that nearly all information posted on Chinese news portals, blogs, forums, social media sites between 1995 and 2005 was no longer available.

“The Chinese internet is collapsing at an accelerating pace,” the headline said. Predictably, the post itself was soon censored.

“We used to believe that the internet had a memory,” He Jiayan, a blogger who writes about successful businesspeople, wrote in the post. “But we didn’t realize that this memory is like that of a goldfish.”

It’s impossible to determine exactly how much and what content has disappeared. But I did a test. I used China’s top search engine, Baidu, to look up some of the examples cited in Mr. He’s post, focusing on about the same time frame between the mid-1990s and mid-2000s.