I believe I’m having a similar issue when my metahuman’s right hand moves too closely to the mesh over him.
I believe it has something to do with how it’s colliding with the mesh and not anything with shadows. But I’ve tried increasing the mesh bounds and even disabling shadows in the level outliner, but nothing works. It might also have to do with volumetric shadow mapping, since I see the effect to a greater degree when applying those viewing filters.
No idea what to do about it yet.