@theluthier this is something that has bothered me for some time and I think I know what is happening; sometimes when you have a curved surface (which is almost always when applying hair), there are some Hair Particles, that have their Roots below the Surface:

As you can see, that only happens in certain places. And when you make the Hairs really short, some will not reach the Surface.
It took me quite some time to figure this out, but when you Triangulate the Mesh, things become clear:

There were non-planar quads and the Hair position was being calculated on the Triangulated Mesh.
Checking the Hoodie revealed many non-planar quads (I just highlighted a few, but they are everywhere):

My guess is, that that causes the bare patches of fuzz.
Not sure how to resolve that, considering the Multires Modifier…