It sounds to me like a loading problem. 35mm films, especially 36 exposure, are pretty long, barely a degree or so of misalignment at the start can throw things pretty far out of kilter by the time you get to the far end. Some SS reels (Hewes!) are easier to load than others. And old/used reels that may have been dropped can add problems from an almost unnoticeable bend in the spiral.

In the midst of a long ago discussion, I measured the spacing between the spirals at four different points around the circumference on my 120 reels and discovered the tolerance on the el-cheapo that makes me crazy was about four times sloppier than the Hewes that usually works like a charm. That seems to confirm it wasn't just my imagination. But lots of practice helps too. Films with unusually large amounts of curl can be frustrating also. After you do more of it, you may recognize the feel, and even the sound of the film edges scraping past the spiral that can indicate whether or not things are going correctly.

I remember once after ten minutes of frustration stuffing the bare film in the tank, putting the lid on and taking a half hour break. Thankfully it went better on the second pass!