Multiple things could cause these small raised sections.
Shingles bumps on roof.
In the photo shown here some blister tops have lost granules and are beginning to expose the shingle interior substrate.
In some cases moisture can get trapped within the shingles during the manufacturing process.
Lets start with the small random bumps on your roof.
Blisters in shingles or rash blisters are a cosmetic defect in the opinion of some roofing manufacturers and an indicator of reduced shingle life in the opinion of some building professionals.
Blistering can also happen as a result of poor ventilation.
Most commonly know as nail pops these areas are caused by either a roofing nail not being driven all of the way in or one that gets driven in side ways and will hold the shingle up just slightly.
Overheating or thermal shock in addition to blisters overheating can cause other roof deformities such as warped decking or trusses which can push the shingles up into ridged or undulating formations.
Properly vent the attic.
Once the vapors contract or the moisture evaporates the blisters should just disappear without causing any real damage to the roof.
When the sun heats the shingle the trapped moisture will rise to the surface causing the tell tale blistering.
Asphalt shingles can blister as a result of trapped moisture in the shingles.
As long as it.
Excess moisture must be allowed to exit the roofing system.
After it dries the roof should be flat again.
For every 150 square feet of.