The answer to 'why is my flashing missing shingles' is that the flashing around your roof's edges has become damaged or dislodged, causing the shingles in that area to come loose and fall off. This is a common issue that can be caused by age, weather, or improper installation.
Some common symptoms include visible gaps or holes in the flashing, shingles that are curling or falling off, and leaks or water damage around the roof edges. The solution is to inspect the flashing, make any necessary repairs or replacements, and then properly re-secure the shingles in that area. This is usually a job best left to a professional roofer, as it requires specialized skills and safety equipment.