I shot a film test with Tri-X tonight. All the frames came out just fine, using my normal agitation and development style. I really don't think this could be a development problem, especially since the frames with these problems have clear edges.
So that means it is looking like a camera or a lens issue and possibly cold related. I opened the back and cycled the shutter and don't see any problems. Ditto with the lens, everything appears normal. I'll inspect the film back a little closer and compare it to the other ones that I own.
I just can't think of how light could be getting blocked from the sides of the frames, which is the top and bottom of the film in the camera. Is my film buckling in the cold?