To update this for Skyrim SE, Bethesda added a new setting that controls this:
bDisableShadowJumps toggles whether or not sun-shadow movement is controlled dynamically outdoors, resulting in constantly moving and potentially flickering shadows in relation to the movement of the sun as time passes. Disabling this will result in sun-shadow movement being dictated by the fSunShadowUpdateTime and fSunUpdateThreshold settings, as utilized previously in the non-Special edition version of the game.
Skyrim.ini
[Display] bDisableShadowJumps=0