Monday's market plunge sent investors rushing to check on their accounts, and in some cases, they were temporarily unable to do so.

T. Rowe Price confirmed issues with its website Monday. "We sincerely regret the inconvenience caused by the recent outage and would like you to know that the website is now available," the company wrote on Twitter. "Please be assured that our Technical Support team will continue to monitor the situation to ensure that website accessibility is maintained."

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A spokeswoman for TD Ameritrade confirmed one of its mobile apps that allows customers to access their accounts and make trades was "slow" for a period in the afternoon, but has since been fixed.

The Dow Jones industrial average closed down 1,175 points, but earlier in the afternoon briefly had been down nearly 1,600 points.

On Twitter, some people said they were having problems accessing the websites or mobile apps of robo-advising firms, including Wealthfront and Betterment. Wealthfront tweeted a reply saying it was aware of an issue on mobile and was working to resolve it. Spokesmen for Wealthfront and Betterment weren't immediately available.

And Dow Jones reported that some people were complaining about being unable to log into their accounts on Vanguard's website. A spokesman for the fund giant was not immediately available.