In late morning trade the S&P/ASX 200 Index (ASX: XJO) is on course to end its winning streak. At the time of writing the benchmark index is down 0.4% to 6,700.7 points. Four shares that have fallen more than most today are listed below. Here’s why they are dropping lower: The Appen share price has sunk 12% lower to $26.27 following the release of an update. The artificial intelligence services company revealed that COVID-19 has been weighing on its performance and is expected to lead to it falling well short of guidance in FY 2020. It is now forecasting underlying earnings before interest, tax, depreciation and amortisation (EBITDA) of $106 million to $109 million (or $108 million to $111 million when applying the originally assumed exchange rate). This is down from its previous guidance of $125 million to $130 million.