Last summer we bought a shed and panelled inside with tongue and groove panelling. We put up damp proof and insulation first and then the panels on top. We used panel pins on every third board. Over the winter it seems the wood has expanded causing it to push out in places. How can we fix this and can we prevent it happening again?
Your shed may have shifted. I have a larger shed that had this wood veneer nailed to the walls, and it's shifted somewhat, which warps the paneling.
I would make sure your footings and walls are still level. If they aren't, you can use a car jack (use a car stand for a safety backstop) to raise the shed and add supports to raise it back to level.