NEW YORK (Reuters) – Robinhood Markets Inc, the fintech startup credited with helping popularize trading with millennials, said on Thursday it experienced a major trading outage and that while its systems were back online, it was still working to resolve the problem.

“This morning, customers may have experienced issues with some of our services. We’re starting to see improved performance and are continuing to monitor the issue,” said spokeswoman Lavinia Chirico.

Robinhood, based in Menlo Park, California, has experienced several outages since early March, particularly on days of high trading volumes as the market reacted to news on the economic impact of the coronavirus pandemic.

Similar to previous outages, customers have taken to social media to criticize Robinhood, threatening to switch brokerages.

“Unacceptable for this to keep happening,” one user said on Twitter. “Give me one reason why I should continue to trade using your platform?” asked another.

Robinhood has been at the center of a recent upsurge in day trading by retail investors, who have been homebound due to coronavirus lockdowns.

Founded by co-chief executives Baiju Bhatt and Vladimir Tenev in 2013, Robinhood is one of the most popular and well-funded financial technology startups. Last month, it raised $280 million from investors at a valuation of $8.3 billion dollars.

The company now has over 10 million user accounts. Customers at the brokerage, which has been credited for helping usher in commission-free trading throughout the retail brokerage industry, have a median age of 31, the company said recently.