Roofing problems can be tricky to diagnose and solve but the solution here should be pretty straightforward.
Roof plywood buckling.
Most underlayments have an adhesive side and a barrier side.
When these boards are not properly fastened and nailed to the framing they can.
Plywood and osb roof sheathing are the most popular roof sheathing materials in the u s.
The nails slip out of the sheathing and create small visible bumps on the surface of your roof.
Your roof decking is the plywood sheets that cover your home.
A roof over or re roof is not recommended because it will certainly lead to buckling.
For a good reason.
Wood expands and contracts so there may not have been adequate planned spacing.
Buckling roof plywood below asphalt shingles is a result of many things.
If the adhesive side is not laid properly and not applied flat it will surely show its buckling through the roof shingles.
They are easy to work with readily available and perform the job well.
I agree that it looks as if the buckling is at sheathing butt joints at rafters.
Buckling can occur if the wrong type of nails were used to connect the sheathing to the rafters.