The answer to 'why is my flashing sagging' is that the flashing has become loose or detached from the roof or wall. This can be caused by factors like poor installation, weathering and aging, or physical damage from weather or other external forces. Sagging flashing is a common roofing problem that needs to be addressed promptly to prevent further damage and leaks.
Symptoms of sagging flashing include visible gaps or separation between the flashing and the roof or wall, as well as water stains, mold, or other signs of moisture intrusion around the flashing. To fix sagging flashing, the cause needs to be identified and the flashing properly re-secured or replaced. This may require removing and reinstalling the flashing, or replacing deteriorated sections.