There were many, and varied things missed in my inspection. The biggest was the entire HVAC system being messed up. The furnace was incorrectly installed, improperly sized for the house, and didn't even have any return ductwork installed.
The air flow seemed really bad in the bedroom and so one day I decided to climb up into the attic and take a look. The problem with the return air missing was immediately obvious. When I called the inspector to ask why they'd miss something so obvious I was given an excuse and pointed toward the part of the contract that states they're not liable. I eventually got them to refund the cost of the inspection, but it was hundreds of dollars back for over ten thousand dollars in missed issues. I was only able to get anything because I worked for a real estate company at the time and knew the right people who could apply pressure.
IMO Home inspections are a total scam.