FILE PHOTO: Outside a GameStop store people line up to purchase a Sony PS5 gaming console in the Manhattan borough of New York City, New York, U.S., November 12, 2020. REUTERS/Carlo Allegri

GameStop Corp. dipped in extended trading after rising nearly 70% on Friday, wrapping up a week of wild swings as retail investors returned to the stock after trading restrictions on the company were lifted.

The shares at the center of the retail craze that’s gripped Wall Street and drawn scrutiny from Washington, rallied after Robinhood Markets’ decision to lift some curbs that prevented investors on Thursday from buying the stocks that had been going straight up for days.

GameStop closed the session at $325, wrapping up a 400% price surge in the week. The company’s value quintupled since last Friday despite Thursday’s plunge, which wiped out $11 billion in market cap. Shares in other day-trader favorites snapped back from record losses as well.

Worth less than $5 billion just a week ago, GameStop has been propelled by day traders using Reddit forums to take on the Wall Street establishment. At one point, the company briefly became the largest member of the Russell 2000 Index after hitting a peak value of $33.7 billion Thursday. The retailer was worth $22.7 billion at the close on Friday.

In after-hours trading — when most retail investors are restricted from trading — GameStop shares fell 4.6% while a few other Reddit favorites also declined including Siebert Financial Corp., Express Inc. and Naked Brands Group Ltd.

“The trading restrictions helped a bit but the rules will need to be refined such that it does not just restrict one class (i.e. retail) of investors,” said Amy Kong, chief investment officer of Barrett Asset Management. “At some point, like a house of cards, this will prove unsustainable.”

Citron Capital’s Andrew Left, one of the short sellers who has faced a reckoning in the battle with the growing groups on Reddit’s WallStreetBets forum, said the firm will discontinue offering short-sell analysis after 20 years of providing the service. Left said on Wednesday his firm closed out of a GameStop short bet in “the $90’s at a loss of 100%.”

AMC Entertainment Holdings Inc. pared gains to 54% after rising as much as 85% and Koss Corp.’s rally of as much as 151% was more than halved as it triggered multiple trading halts. AMC has more than tripled in size this week with its market value ballooning to $5.3 billion while Koss shares surged 1,816% this week.

In extended trading, AMC fell 1.6% as shareholder Silver Lake reported it had sold its entire stake. Meanwhile, Koss pared back gains of as much as 14% to trade up less than 2%.

The U.S. Securities and Exchange Commission said it’s looking at potential misconduct and will review decisions by brokerages to curtail buying of some stocks.

Robinhood raised limits Friday on purchases of shares and options contracts for 50 companies including GameStop and AMC. Morgan Stanley’s E*Trade said it expected to resume normal trading operations Friday, while Trading 212, another app, said it enabled trading of GameStop and AMC, two of the stocks whose gains have delivered massive losses to some prominent hedge funds that held large short positions in them.

Robinhood’s decision Thursday to rein in the risk to itself by banning certain trades and unwinding client bets — igniting an outcry from customers and even U.S. political leaders — came after the stock market’s central clearing hub demanded large sums of collateral from brokerages that for weeks had facilitated spectacular jumps in shares such as GameStop. The trading platform also said it was raising an emergency infusion of more than $1 billion from its existing investors.

“This GameStop phenomenon is crazy,” New Jersey Governor Phil Murphy, a former Goldman executive, said. “I’m reminded of an old adage: When people who don’t ordinarily talk about the stock market start talking to you about it like, ‘Hey, did you see the Giants game last night?’ it’s time to sell.”

The prospect of continued volatility driven by retail-trader speculation weighed on stock prices Friday when the S&P 500 Index fell 1.9%. The index had its worst weekly performance since the end of October.