The most likely cause is flare/internal reflections in the lens, especially if it only happens in certain lighting and you also see smaller light artifacts. On a late-1950s camera, lens coatings are less effective than on modern lenses, so strong side light can produce a washed-out circular flare like this.

First thing to try: use a lens hood or shade the lens from stray light and see if the problem disappears.

Also inspect the lens for debris, since something inside or on the lens can create unusual artifacts.

A second mechanical possibility is a sticky shutter/aperture. Check whether the shutter opens and closes smoothly; hesitation could cause odd exposure patterns. But based on your description—only on some photos, with raking light and additional smaller artifacts—flare is the strongest explanation.