The answer to 'underlayment damaged' is that the most common causes are water damage, wear and tear, or improper installation. Symptoms may include leaks, mold growth, or deterioration of the roof surface. The solutions can range from minor repairs to full underlayment replacement, depending on the extent of the damage.
For minor issues, a homeowner may be able to DIY the repairs. However, for more significant damage or if you're unsure of the extent of the problem, it's best to call in a professional roofing contractor. They can properly assess the situation and recommend the best course of action to restore your roof's integrity and prevent further issues.