Just a thought...
Are you talking about the little "notch" shaped details at the corners of the frames?
A couple of my cameras do that. I presume it's a small defect in the aperture plate inside the camera.
While they shouldn't have major defects, a company can't manufacture thousands or millions of cameras over a period of years to decades without having some variation.
Even if they were manufactured perfectly every time (and they should be VERY close) over the years, wear and tear might have taken its toll.
I look at it like the rifling in the barrel of a gun. No two are exactly alike.
In fact, I can tell if a roll of 120 was shot in my Yashica or my Rolleiflex just by looking at the details in the corners of my negatives.
The Yashica has an ever-so-sleight "dart" in the corner of the frame. Similar to yours, only smaller.
I'm not saying all cameras have this. In most cameras that do have small defects in the aperture, you probably couldn't tell unless you used a magnifier.
Regardless, it's probably worth checking your camera over. Look at the aperture plate, the lateral film guides, the pressure skid and the film trap area, in general. It might be simple as a piece of crud stuck in the corner that causes the film to buckle.
I'm not sure this is the case with your camera but, for two minutes worth of cleaning and checking, you've got nothing to lose.