BEIJING — Everybody knew where Justin Sun, a brash Chinese millionaire and cryptocurrency celebrity, was going to be this week. He had paid a record $4.6 million to have a charity lunch with Warren Buffett, the investing guru, in San Francisco, and he was counting down the days on social media.

Then Mr. Sun, citing ill health, postponed the lunch three days before it was to happen, sending the Chinese media and internet into overdrive. One outlet reported that he would be held in China once he returned while the authorities investigated his financial dealings. Another asserted that he had never left China in the first place .

Mr. Sun denied it all on social media, posting photos and a video of himself with San Francisco landmarks in the background. But the reports, while sounding as though they had been ripped from the pages of an overwrought thriller, were not without precedent.

As the Chinese authorities take an increasingly heavy-handed approach to policing the business and financial worlds, executives have been known to disappear for months and even years.