These were processed and scanned by a lab, right? It looks like there is a hair on the lab's scanner glass. Given that it's white on a scan from neg, we know the hair is recorded post-exposure (if it was blocking light pre-exposure, it would appear as black in the final image). So I don't reckon there's hair in the camera unless it's magical glowing hair or something.

That darkness in the upper-right corner looks like you used a polariser, which can cause unevenness in skies. It could also be uneven shutter curtain speed (the building looks a little darkened too...), e.g. if the first curtain opens a little slowly in one direction, you will get darkness on that side. If the shutter speed is uneven, try looking through the shutter at flashed white surface. If the shutter slit at high speed is narrower on one side than the other, then there's your problem. It will be very difficult to setup a test where you can directly observe this though.

If you don't mind burning a little film (2 frames!), and assuming the shutter is the typical reversing kind (moves one direction then the other on alternating frames), there is a simple test that has a chance of working. Point a flash and the camera at a white wall and take two consecutive photos at 1/1000. The flash should appear as a stripe across the frame (you are way above x-sync here) and on consecutive photos, it should appear on opposite sides of the frame. If the flash stripes are recorded as different widths, you know it's a shutter-unevenness problem.

Before you do that though: are the darkened frames all odd-numbered or all even-numbered? If not, then you may have some other problem.