Trading app Robinhood has suffered another trading outage, on one of the most important days for trading in the past decade.

At 2.06 PM UTC today, Robinhood tweeted that trading was down and that it was investigating the issue. It has since tweeted that trading has been partially restored. But it couldn't have come at a worse time for traders.

Stocks were hit today in the worst day of trading since the financial crisis. The price of oil fell by nearly 30% and major stock market indexes are down by seven percent.

And traders were furious. "I just can't believe this. Two Mondays back to back during the most important moments. There could not be any worse of a time for the system to go down. Literally it could not be any worse than this," one wrote on Twitter.

It’s the latest in a succession of issues faced by the exchange, following an earlier outage on March 2 that lasted through the night. At the time, Robinhood tweeted that, “When it comes to your money, issues like this are not acceptable.”

That outage was also on a day of increased trading volume that saw the Dow Jones gain over 1,200 points.

Robinhood is also a popular trading app for cryptocurrencies, ,any of which have seen high volatility today. The price of Bitcoin (BTC) has dropped 10%, and many other top ten coins have posted double digit losses.