Confusion with stationary light dynamic shadows vs. movable light

Hi, ran into some ugly shadowing using a stationary spotlight over a movable object, and I’m wondering if there’s something i’m missing to get them to look nicer. Tweaking shadow bias helps a little, but it’s still too ugly for use. The worst thing is the artifacts change drastically as you move closer to the door, as if I’m passing through shadow cascades. The picture below was taken about 500 cm away from the door, with default shadow settings on the light, production lightmass build, and epic settings for everything.

The light is a standard spotlight set to stationary, with default shadow settings. The object is an animated skeletal mesh with a very basic white glossy material applied.

My confusion only increased when I set the light to movable. The artifacts went away, and the shadows appeared as intended, as shown in the next picture below. (also, shadow bias can be set to nearly 0 on the movable light before any artifacts appear)

I would have expected both the stationary and movable lights to produce similar looking shadows on the dynamic object. Clearly something else is happening with the shadows here, and I don’t understand what it is I’m seeing. Does anyone have any insight or can tell me what might be going on?