Robinhood struggled to handle huge volumes of stock trading and sparred with its principal customer, market maker Citadel Securities, during the week in January 2021 when meme stocks exploded, according to a report from the Democratic staff of the House Financial Services Committee.

The committee held hearings in February 2021, questioning the chief executives of Robinhood and Citadel Securities, as well as meme-stock hero Keith Gill and Gabe Plotkin, the hedge-fund manager who lost billions betting against GameStop and other hot stocks. The staff reviewed tens of thousands of pages of internal documents, including pointed communications inside and between the companies.