In response, several large ad agencies and brands, including General Motors and Volkswagen, paused their ad spending on Twitter. Mr. Musk has said Twitter was on track to post $3 billion in revenue in 2023, down from $5.1 billion in 2021, when it was a public company.

Twitter’s valuation has since plunged. In March, Mr. Musk said the company was worth $20 billion, down more than 50 percent from the $44 billion he paid for it. Last week, the mutual funds giant Fidelity, which owns shares in Twitter, valued the company at $15 billion.

Twitter feels increasingly “unpredictable and chaotic,” said Jason Kint, chief executive of Digital Content Next, an association for premium publishers. “Advertisers want to run in an environment where they are comfortable and can send a signal about their brand,” he added.

Some of Twitter’s biggest advertisers — including Apple, Amazon and Disney — have been spending less on the platform than last year, three former and current Twitter employees said. Large specialized “banner” ads on Twitter’s trends page, which can cost $500,000 for 24 hours and are almost always bought by large brands to promote events, shows or movies, are often going unfilled, they said.

Twitter has also run into public relations snafus with big advertisers like Disney. In April, Twitter mistakenly gave a gold check mark — a badge meant to signify a paying advertiser — to the @DisneyJuniorUK account, which Disney doesn’t own. The account posted racial slurs, leading Disney officials to demand from Twitter an explanation and assurances that it wouldn’t happen again, two people with knowledge of the situation said.