I have noticed that when rendering multiple viewports in the same tick that one of the viewports will smear moving skeletal meshes when Temporal Super Resolution or Temporal Anti Aliasing is enabled. My guess is that there is some cache somewhere that is built per frame from a single view and is then only refreshed on the next tick.
This can be recreated by adding a camera to a level with an animated skeletal mesh in and pressing simulate, then selecting the camera to view the preview. Either the preview or the main viewport will render with smearing instead of motion blur.
This can also be recreated with other render pipelines such as using an Off World Live Capture Camera while rendering the main viewport. Does anybody have any workarounds? It has been suggested to disable Custom Depth with TemporalAA Jitter but this has not had a noticeable improvement.