> By the way, why didn't this happen with 35mm movie projectors? They couldn't blend adjacent frames either, because they are just shining light through individual pictures on a sheet of celluloid, yet I don't remember seeing this kind of stutter in movie theatres back in the day!

Normally you’d shoot at 180 degree shutter angle (exposure time is half the frame time). This produces a “cinematic” blur that doesn’t look choppy, especially when projected at the same rate. So if you’re shooting 24 fps video, try shooting at 1/48. This is slow compared to most handheld still photography, which is why you start to need ND filters on cine cameras, especially if you also want to shoot wide open.

Stutter is particularly noticeable for fast panning landscapes where there’s uniform motion across the entire frame. Very obvious if there are “gaps” in the blur because your brain will want to interpolate. If there are static/foreground objects, you probably won’t notice.