In one of the YouTube videos from Mr. Zhang, the China National Radio employee, a character in the description is incorrectly translated into traditional Chinese from simplified Chinese. Mr. Zhang did not respond to a message seeking comment.

Puma Shen, an assistant professor at National Taipei University who studies Chinese influence efforts, does not believe that disinformation from China is always guided by some central authority as it spreads around the internet.

“It’s not an order from Beijing,” Mr. Shen said. Much of the activity seems to be scattered groups of troublemakers, paid or not, who feed off one another’s trolling. “People are enthusiastic about doing this kind of stuff there in China,” he said.

In December, Taiwan’s justice ministry warned about a fake government notice saying Taiwan was deporting protesters who had fled Hong Kong. The hoax first appeared on the Chinese social platform Weibo, the ministry said, before spreading to a Chinese nationalist Facebook group.

Sometimes, Chinese trolls amplify rumors already floating around in Taiwan, Mr. Shen said. He is also on the lookout for Taiwanese social media accounts that may be bought or supported by Chinese operatives.

Ahead of midterm elections in 2018, his team had been monitoring several YouTube channels that discussed Taiwanese politics. The day after voting ended, the channels disappeared.

After Yu Hsin-Hsien was elected to the City Council that year in Taoyuan, a city near Taipei, mysterious strangers began inquiring about buying his Facebook page, which had around 280,000 followers. Mr. Yu, 30, immediately suspected China.