Medicare Advantage is a super-popular alternative to traditional Medicare, but some experts say it has a hidden flaw that could break the system. People love the program because many of its plans have zero-dollar premiums (after the standard Medicare Part B premium), benefits that traditional Medicare doesn’t offer, and lower out-of-pocket spending. About 36 million Americans are enrolled. But there’s a catch. A series of lawsuits by the Department of Justice has exposed a problem that cost taxpayers billions of dollars, according to the Department of Health and Human Services inspector general. Simply put, health insurance companies get paid more for enrolling sicker people into Medicare Advantage. That gives them a perverse incentive to identify diseases without treating them....