I have a relatively simple mesh, that looks like this (a couple of tight faces and loop cuts due to subdivision smoothing):
However when I try to UV unwrap it, it's a whole mess and even misses most of the faces:
When I select a face I can see where it is located on the texture map:
But other faces aren't located on it at all:
What could have went wrong here?
I made sure to select all vertices of the mesh before unwrapping, so I don't think that's the problem.