In March, Super Micro Computer was added to the S&P 500 after an epic run that lifted the stock by more than 2,000% in two years, dwarfing even Nvidia’s gains.

As it turned out, S&P was calling the top.

Less than two weeks after the index changes were announced, Super Micro reached its closing high of $118.81 and had a market cap of almost $70 billion. The stock is down 72% since then, pushing the valuation to under $20 billion, the first major sign in the public markets that the hype around artificial intelligence may not all be justified.

Super Micro is one of the primary vendors for building out Nvidia-based clusters of servers for training and deploying AI models.

The stock plunged 33% on Wednesday, after the company disclosed that its auditor, Ernst & Young, had resigned, saying it was “unwilling to be associated with the financial statements prepared by management.” It was down another 16% on Thursday.

Super Micro is now at risk of being delisted from the Nasdaq, and has until Nov. 16 to regain compliance with the stock exchange.

“We see higher delisting risk in the absence of an auditor and the potential challenge to getting a new one,” analysts at Mizuho, who have the equivalent of a hold rating on the stock, wrote in a report Wednesday.

Ernst & Young was new to the job, having just replaced Deloitte & Touche as Super Micro’s accounting firm in March 2023.

A Super Micro spokesperson told CNBC in a statement that the company “disagrees with E&Y’s decision to resign, and we are working diligently to select new auditors.”

Representatives for Ernst & Young and Deloitte didn’t respond to requests for comment.

For much of Super Micro’s three decades in business, the company existed well below the radar, plodding along as a relatively obscure Silicon Valley data center company.

That all changed in late 2022 after OpenAI’s launch of ChatGPT set off a historic wave of investment in AI processors, largely supplied by Nvidia. Along with Dell, Super Micro has been among the big tangential winners in the Nvidia boom, packaging up the powerful graphics processing units (GPUs) inside customized servers.

Super Micro’s revenue has at least doubled in each of the prior three quarters, though the company hasn’t filed official financial disclosures with the SEC since May.

Wall Street’s mood on the company has shifted dramatically.

Since the S&P’s announced index changes in March, Super Micro’s stock has dropped at least 10% on several separate occasions. The most concerning slide, prior to Wednesday, came on Aug. 28, when the shares sank 19% after Super Micro said it wouldn’t file its annual report with the SEC on time.

“Additional time is needed for SMCI’s management to complete its assessment of the design and operating effectiveness of its internal controls over financial reporting as of June 30, 2024,” the company said.

Noted short seller Hindenburg Research then disclosed a short position in the company, and said in a report that it identified “fresh evidence of accounting manipulation.” The Wall Street Journal later reported that the Department of Justice was at the early stages of a probe into the company.

The month after announcing its report delay, Super Micro said it had received a notification from the Nasdaq, indicating that the delay in the filing of its annual report meant the company wasn’t in compliance with the exchange’s listing rules. Super Micro said the Nasdaq’s rules allowed the company 60 days to file its report or submit a plan to regain compliance. Based on that timeframe, the deadline would be mid-November.

It wouldn’t be the first for Super Micro. The company was previously delisted by the Nasdaq in 2018.

Wedbush analysts see reason for worry.

“With SMCI having missed the deadline to file its 10K and the clock ticking for SMCI to remedy this issue, we see this development as a significant hurdle standing in the way of SMCI’s path to filing in time to avoid delisting,” the analysts, who recommend holding the stock, wrote in a report.

As Super Micro’s stock was in the midst of its steepest sell-off since 2018 on Wednesday, the company put out a press release announcing that it would “provide a first quarter fiscal 2025 business update” on Tuesday, Nov. 5.

That’s Election Day in the U.S.

Super Micro’s spokesperson told CNBC that the company doesn’t expect matters raised by Ernst & Young to “result in any restatements of its quarterly financial results for the fiscal year ended June 30, 2024, or for prior fiscal years.”

The selloff continued on Thursday, with the stock falling to its lowest level since January. Analysts at Gordon Haskett called the Ernst & Young news a “backbreaker,” while Argus Research downgraded the stock, in the intermediate firm, to a hold, citing the Hindenburg note, report of the Justice Department investigation and the departure of Super Micro’s accounting firm.

“The company’s loss of its auditing firm and the DoJ investigation mean that the stock no longer trades on fundamentals,” Argus analyst Jim Kelleher wrote.

Beyond Super Micro, the evolving incident is a potential black eye for S&P Dow Jones. Since Super Micro replaced Whirlpool in the S&P 500, shares of the home appliance company are down about 3%, underperforming the broader market but holding up much better than the stock that took its place.

Inclusion in the S&P 500 often causes a stock to rise, because money managers tracking the index have to buy shares to reflect the changes. That means pension and retirement funds have more exposure to the index’s members. Super Micro shot up 19% on March 4, the first trading day after the announcement.

A spokesperson for S&P Global said the company doesn’t comment on individual constituents or index changes, and pointed to its methodology document for general rules. The primary requirements for inclusion are positive GAAP earnings over the four latest quarters and a market cap of at least $18 billion.

S&P is able to make unscheduled changes to its indexes at any time “in response to corporate actions and market developments.”

Kevin Barry, chief investment officer at Cantata Wealth, says greater consideration should be given to a stock’s volatility when additions are made to such a heavily tracked index, especially given that tech already accounts for about 30% of its weighting.

“The chances of a stock going up 10 or 20 times in a year or two and then having an indigestion moment is extremely high,” said Barry, who co-founded Cantata this year. “You’re moving out of a low-volatility stock into a higher-volatility stock, when tech already represents the largest sector by far in the index.”

— CNBC’s Rohan Goswami and Kif Leswing contributed to this report.