Charlie Munger’s opinion of Robinhood Markets Inc. hasn’t improved in the past year. If anything, it has become more negative.

The vice chairman of Berkshire Hathaway Inc. blasted the trading platform while addressing thousands of shareholders at the company’s annual gathering in Omaha, Neb., on Saturday. He said Robinhood is losing ground since going public in July 2021. 

“It was pretty obvious that something like that was going to happen,” Mr. Munger said, during a question-and-answer session with Warren Buffett, Berkshire Hathaway’s chief executive and chairman. 

“All the short-term gambling and big commissions and hidden kickbacks and so and so on. It was disgusting,” Mr. Munger said. 

Mr. Munger has criticized Robinhood previously. In a February 2021 interview with The Wall Street Journal, he compared the platform to racetrack betting and said it was wildly speculative. 

Mr. Buffett reminded him of those earlier remarks on Saturday. 

“And now they’re unraveling. God is getting just,” Mr. Munger said. 

His comments came two days after Robinhood said its revenue fell to $299 million in the first quarter, a decline of 43% from the same period last year. It was the company’s fifth-consecutive quarterly drop. 

The online trading app, which says it offers a commission-free experience, also said last week that it would lay off 9% of its full-time workers. 

Jacqueline Ortiz Ramsay, head of public policy for Robinhood, hit back at Mr. Munger’s most recent comments.

“It is tiresome witnessing Mr. Munger mischaracterize a platform and customer base he knows nothing about,” she said in a written statement. “He should just say what he really means: unless you look, think, and act like him, you cannot and should not be an investor.” 

Her statement this weekend echoed the response she gave more than a year ago when Mr. Munger began criticizing Robinhood over the way it had enabled and profited from the January 2021 individual-investing boom. 

“In one fell swoop an entire new generation of investors has been criticized and this commentary overlooks the cultural shift that is taking place in our nation today,” she said at the time. 

Robinhood signed up millions of investors during the Covid-19 pandemic. Now it is struggling to hold on to them. The number of monthly active users on the platform fell 10% in March, compared with the same month a year earlier. 

The company doesn’t charge brokerage fees, instead relying on trading volume for revenue. It sends customer orders to high-speed trading firms in exchange for cash, in a practice called payment for order flow. 

Shares in Robinhood fell 2.8% to roughly $9.81 on Friday. The shares have fallen nearly 47% this year. 

Mr. Buffett asked Munger whether it was wise to be so openly critical, to which Mr. Munger answered: “Probably not. But I can’t help it.”

Akane Otani contributed to this article.

Write to Ginger Adams Otis at Ginger.AdamsOtis@wsj.com