Robinhood took out full-page ad in Tuesday's Times saying it is 'humbled' Online brokerage faces scrutiny after limiting the purchase of certain stocks Robinhood struggled to meet deposit requirements at clearinghouses last week Now executives will have to appear before Congress in hearings on the matter It came as small investors on Reddit drove a buying frenzy in 'meme stocks' GameStop shares dropped in early trading Tuesday, as AMC and silver also slid