Robinhood, the free-trading pioneer favored by younger traders, said it experienced an outage Monday.

The technical problems took up most of the trading day and were not fixed before the close. Robinhood clients missed out on the biggest one-day point gain in the Dow Jones Industrial Average in history.

"We are experiencing a system-wide outage. We are working to resolve this issue as soon as possible," the company said in a message to clients Monday. With an hour left in the trading day, Robinhood updated clients saying, "the issue has been identified and a fix is being implemented."

The outage came amid the market's attempt at a rebound from the worst week for stocks since the financial crisis fueled by investor panic surrounding the fast-spreading coronavirus. All three major averages climbed on Monday, closing out of correction territory. The Dow Jones Industrial Average gained nearly 1,300 points, the most ever in a single session.

The Silicon-Valley start-up gained popularity with young investors by offering free stock trading in 2013. The Menlo Park, California-based company said in December that it has 10 million users on the platform.

"Your portfolio information is not available right now. Please check back later," read a Robinhood message to clients posted Monday on Twitter. Many other tweets showed the app with a blank, white screen.

News of Robinhood's outage came a week after Fidelity and Charles Schwab said they had technical difficulties amid an 800-point plunge by the Dow Jones Industrial Average. TD Ameritrade also said some of its clients were experiencing technical issues at that time last week.

One factor possibly contributing to these platforms' technical issues could be higher-than-average trading volumes. Last week, the SPDR S&P 500 ETF Trust (SPY) traded more than 200 million shares three times. On Friday, shares of the ETF changed hands more than 385 million times. Those numbers are well above the SPY's 30-day average volume of 97.3 million shares.

Robinhood kicked off a wave of fee slashing in the broader brokerage industry with Charles Schwab, TD Ameritrade and Fidelity dropping commission fees late last year.

"We're experiencing downtime, and are working to resolve this as quickly as possible," a Robinhood spokesperson told CNBC.

Users took to twitter to air their concerns about staying on the sidelines during the market rally on Monday.

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— With reporting from CNBC's Fred Imbert and Kate Rooney.

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