I am adding Timewarp to slow down a shot. Inside the shot an actor is moving his hand. His hand waves in front of a bush. The time warp is distorting the image all around the moving hand, particularly the bush behind it. I tried at 50% and 25%. The slower it is, the worse it is, but it is still present at 50%.
Timewarp with FluidMotion recreates frames based on pixels and motion vectors in the image. Artifacts usually occur when something is being revealed that wasn't in the previous frame. This is what the vector map editor is for - a bit daunting, but you will see all the vectors and movement as color maps and can keyframe the mesh as needed.