The answer to 'soffit sagging' is that the most common causes are improper installation, wood rot, or water damage. Symptoms include the soffit (the material under the roof's overhang) sagging, cracking, or pulling away from the home. Solutions depend on the severity, but may involve replacing damaged soffit panels, reinforcing the framing, or addressing any underlying moisture issues.
If the sagging is minor, you may be able to fix it yourself by securing the soffit back into place with fasteners. However, for more extensive damage or if you're unsure of the cause, it's best to call a professional roofing contractor. They can properly diagnose the issue and make the necessary repairs to prevent further damage to your home.