My wife broke her ankle, spent the night in the hospital hooked up to IV pain meds, and had surgery the next day.

Insurance said that the overnight stay was medically unnecessary, as the care could have been provided in a more appropriate setting. They only approved overnight stays in instances where the patient's pain needed constant management or they were having surgery. Bonus points: there was a footnote on the denial papers saying that the person who denied the coverage had a medical background...in OBGYN. Not orthopedics.

Spent literally months appealing that before they begrudgingly agreed that it was covered, which makes us the lucky ones in the US Healthcare system.