A couple reasons your shingles seems to be buckling together are
1. Moisture underneath shingles typically in underlayment such as tar felt
2. Plywood underneath was installed to tight where one plywood’s meets the next horizontally on the vertical gap, There should be a gap between sheets.
3. Attic ventilation is not adequate, Ensure you have enough exhaust and intake ventilation to keep attic cool in the summer time and dry in the winter time
4. Asphalt shingles where installed butted next to each other with no gap in-between to allow for expansion and contraction in changing climates.
5. Asphalt shingles were installed with a hump in between, This hump is usually caused by setting the roof bundles lay over ridge and causing them to bend and simulate a curve in between when installed.
6. Loose plywood ends could pry up and raise shingles causing them to buckle
7. A offset raised rafter can cause the shingles to raise and buckle
All of these problems can be fixed and prevented with the help of a experienced professional.
