Alcoa Corp. announced a reduction in its alumina production forecast, citing operational issues at its Australian refinery. This news led to a significant drop in the company's share price.

The issues at the refinery specifically impacted alumina output, a key component in aluminum production. Despite these operational challenges, Alcoa reported that higher aluminum prices during the quarter did contribute to an increase in overall revenue.

However, the negative impact of the reduced alumina output and the associated operational problems proved to be a stronger market signal, overshadowing the positive revenue figures. Investors reacted negatively to the production forecast cut, leading to the tumble in Alcoa's stock.