Nothing keeps hand nails from backing out.
Nails backing out of roof.
If it is just in the area of the the spar you showed us then it might be further evidence of past damage.
Joined sep 17 2008.
Usually the cause is the nail falling in a crack such as sheathing joints or probably in your case cracks between the rake trim and roof if you have old t locks that were face nailed to hold the ends down they always work out it would be easy to peel a shingle back on the edge to see if this is the problem.
It is vitally important that roofing nails of the correct length were used to secure the shingles.
Roofing nails backing out.
That keeps the gun nails from backing out of the wood.
Also is that the only place you have an issue with nails backing out or are they backing out all over.
But what is difficult is keeping the slick sided hand nails from backing out of the roof decking.
Nail is backing out of decking and pushing through the shingle causing a penetration point for moisture.
Apart from roofing shingles roofing nails can sometimes back out.
There are all sorts of reasons why nails back out of seemingly solid wood but perhaps the most common reason is that the nail did not get a good bite into the wood when it was first driven.
If you have a friend in the attic ask him to direct you to a sturdy spot where the nail can bite into the wood.
A gun nailed roof properly installed is a better roof than a hand nailed roof.
This leaves small holes that water can easily penetrate and leave your shingles unstable.
Hammer a new nail into the roof about 1 inch above the hole from the previous nail.