It was almost always indoors, so that might have been it. I just did an experiment: I turned on a fan I have in my room, while no electric lights were on (only sunlight through the window). Looking at the blades, they indeed seemed like a blur that didn’t resolve into individual blades. However, when I changed the speed of the fan, it seemed like a part of the blur resolved into a bunch of blades that slowed down their spin and changed directions. The blades didn’t fully resolve into visibility, and there were more blurry kind of visible blades than there should have been blades in the fan, but it was very clearly happening (multiple times as I changed the speed back and forth, though not every time I changed the speed). Weird.
It was almost always indoors, so that might have been it. I just did an experiment: I turned on a fan I have in my room, while no electric lights were on (only sunlight through the window). Looking at the blades, they indeed seemed like a blur that didn’t resolve into individual blades. However, when I changed the speed of the fan, it seemed like a part of the blur resolved into a bunch of blades that slowed down their spin and changed directions. The blades didn’t fully resolve into visibility, and there were more blurry kind of visible blades than there should have been blades in the fan, but it was very clearly happening (multiple times as I changed the speed back and forth, though not every time I changed the speed). Weird.
Yeah, I can’t check right now, but my guess is some electrical effect when changing fan speed.