Foil can create more problems than it solves
Placing foil directly on the oven floor can trap heat, interfere with airflow and, on some models, damage enamel or components below the floor. The exact risk depends on the oven design, so the manufacturer instructions take priority.
Safer cleanup habits
Use oven-safe cookware to catch spills when appropriate and clean spills using the methods approved in the manual. If foil has melted or bonded to a surface, avoid aggressive scraping that could damage the finish.
Safety note: Appliance symptoms can have more than one cause. Disconnect power before inspecting electrical components. Do not perform gas-line work or bypass safety devices.