Robinhood isn't sure what's behind its latest outage, which hit during the worst day for the Dow since 2008 and knocked out the app's fractional-share trading for most of the session A Robinhood spokesperson told Business Insider that Monday's outage was not related to the issues that sidelined customers for two days last week . The cause of the latest outage, which began shortly after trading started and plagued the app until 3:30 p.m. ET, is still unknown, according to the spokesperson. Robinhood's cofounders had posted a note last Tuesday night to the trading app's blog blaming last week's system-wide outages that infuriated users on "stress to its infrastructure" from an "unprecedented load." A Robinhood spokesperson said the company was now working internally and with its partners to understand the problem. In October 2018, Robinhood launched its own in-house clearing service, choosing to go it alone as opposed to working with a clearing brokerage, as is the case with many fintechs in the space. Click here for more BI Prime stories. Robinhood is still trying to figure out what caused its latest outage, which crippled the stock-trading startup for most of the trading day on Monday.