The answer to 'roof vent sagging' is that a sagging roof vent is usually caused by improper installation or deterioration of the underlying roof structure. Symptoms include a vent that is no longer level or is dipping down, which can lead to leaks and water damage. The solution typically involves re-securing the vent to the roof or repairing the roof framing beneath it.
In many cases, a sagging roof vent is a sign of a more serious structural issue that requires professional inspection and repair. While some minor adjustments may be possible as a DIY project, it's generally best to have a licensed roofing contractor assess the problem and determine the appropriate course of action.