UnitedHealthcare faces significant challenges, including a government investigation into its Medicare billing practices. The largest private health insurer in the U.S. also deals with employee buyout offers, potential layoffs, and public clashes with investor Bill Ackman. Recent events add to a turbulent year for UnitedHealth Group, which has faced the killing of a top executive, a costly cyberattack on its subsidiary, and high medical costs in its insurance division. UnitedHealth Group's shares have dropped over 20 in the past three months.